Friday, November 15, 2013

Empathy and Moral Decision-Making

In the discussion thread of a recent post ( the one that picked apart the argument that allowing same-sex marriage is a slippery slope to bestiality), JD asked the following question: "Is the good and the right defined as 'whatever provokes a strong empathetic response'?"

My response in that discussion thread was a simple no.

In fact, the answer is obviously no. When my daughter hits her head and starts crying, I have a strong empathetic response. Does it follow that my daughter's hitting her head is good and right? Obviously not. So, it is quite obvious that the good and the right is not defined as whatever provokes a strong empathetic response.

But, of course, JD was guilty in this case of asking a very poorly formed question. What he should have asked is something more along the following lines: "Are the behaviors that I am inspired to perform based on a strong empathetic response always morally good and right?" Or maybe it should have been this: "Is 'morally good or right' to be defined simply as 'whatever I am immediately inspired to do when I have a strong empathetic response'?"

Again, the answer would be no. But the question would gesture towards a more interesting, open-ended question: "What is the relationship between moral empathy and moral decision-making?"

I think there is a very strong relationship between empathy and moral decision-making. In general, those with a poorly developed sense of empathy, or those in the habit of failing to attend to what their empathic feelings are telling them, routinely make worse moral decisions than those who cultivate their sense of empathy and pay close attention to what it has to say.

Empathy is about experiencing things through the perspective of another person. Such a capacity can be more or less finely-honed. That is, you can be bad at it even when you try. You imagine yourself into another person's shoes, but your imagining is pretty consistently dead wrong. As such, you can have a very strong empathetic response that is, at the same time, deeply out of tune with the experiences and feelings and needs of the person you are responding to.

So, even if one did want to draw a close theoretic connection between morality and empathy, the identification JD gestures towards--equating moral action with the action one's empathetic responses urge--would not do. Accuracy of empathetic response has to factor in to any empathy-based theory of morality.

And here's another important point: I might have a very strong and very accurate empathetic response to one person's situation, and be motivated by that response to do something that I would balk at doing were I to empathize with certain other people who are affected by the act. In addition to being more or less accurate, empathy can be more or less expansive in its scope. I can empathize with only white slave owners and have no empathy at all for their slaves, and thereby find myself forcefully defending slavery based on a strong and accurate empathetic connection to the former alone.

So, if you were going to develop a moral theory rooted in empathy, you'd want to understand morality not in terms of what a given person's empathetic feelings happen to urge them to do. You'd want to imagine someone in an ideal condition with respect to empathy--someone whose empathetic capacities are both  finely honed in terms of accuracy and widely expansive in terms of scope.

But even here we run into problems, since there is at least some reason to suppose that I ought to be more empatheticaly responsive to my children than I am to distant peoples, even if we concede that I should strive to have empathy for distant peoples as well. As soon as you begin to consider seriously the idea that some empathetic responses ought to play a larger role in moral decision-making than others, you have to begin to ask yourself on what basis this prioritization should be made. And while I can imagine a really creative moral philosopher coming up with a way for empathy to serve as that basis, the more natural approach is to suppose that there is some standard other than empathy which needs to be admitted into our moral deliberations.

Thus, while I think that empathy plays a huge role in morality, I do not think the best moral theory is one which defines morality as what empathy urges, or even what an ideally empathetic agent would feel an urge to do. I think empathy is a virtue that plays a profoundly important role in the decision-making of anyone who hopes to be truly moral. But I think there are other moral virtues that aren't reducible to empathy. A sense of fairness is going to interact with the urgings of empathy in interesting and important ways. Likewise for a sense of loyalty to those with whom one has established deep personal ties and commitments.

And when the urgings of empathy conflict with those of loyalty or fairness, how do you decide what to do? There are no easy answers here. Hence, even when I read JD's question charitably and try to get at what he meant to ask, the answer remains no.

But that said, empathy is important to moral decision-making in all sorts of ways.

Let me count them.

First, without empathy we make decisions based wholly on how things look from our own perspective. Empathy allows us to discern how things look from the perspectives of other people. The more widely we empathize, the more multifaceted our picture of things becomes. The truth about our world is best arrived at when we see things through multiple perspectives. And any kind of decision-making is benefited from a deeper insight into the truth.

Second, empathy gives us a better sense of how actions will affect others at the level of their feelings and their needs. And while I don't think morality can be reduced to making people feel good, there is no question that how actions affect people at the level of emotions and needs-fulfillment is crucial information for sound moral decision-making.

Third, I think morality is fundamentally connected with love. It's about loving our neighbors as ourselves.

As ourselves. One thing about my love for myself is this: I experience my emotions, my desires, my needs. They influence me because I feel them. Empathy takes me out of my head in such a way that I can relate to others in something like the same way that I relate to myself: Their needs and emotions come to have (at the ideal) the same kind of immediacy, the same kind of pull, that mine have for me. While empathy may not be all there is to loving my neighbor as myself, it is a huge piece of it.

Until I can experience the world through my neighbor's perspective, I cannot love my neighbor as I love myself. Until their perspective has a pull on my decision-making--the kind of pull that strong empathetic responses produce--I cannot love them as I love myself. Part of loving someone is experiencing their feelings and needs as something that matters for its own sake, as a reason to act--albeit not a decisive one, but a reason nonetheless, to be weighed against other reasons.

Until I care about the way that a decision will affect my neighbor in something like the way I care about the way it affects me, my decision-making is not shaped by love for my neighbor. And empathy is the chief pathway, if not the only pathway, to such care. Hence, if (as Christians certainly should) you think that moral decision-making must be loving, you can't engage in moral decision-making unless you empathize.

Thursday, November 14, 2013

A Final Thought on Slippery Slopes: Sibling Marriage and Hermann Lotze

My recent posts on slippery slope arguments in the same-sex marriage debate inspired James McGrath, over at Exploring Our Matrix, to take up the topic--and there's been an interesting discussion in the comments section of that post which readers here may want to check out.

One of the commenters, "Straw Man," laid out the following argument, after agreeing that opposition to same-sex marriage is based largely on bigotry:

 Consensual relationships between *adults* who happen to be blood relations are generally condemned, but it's impossible where I sit to see a rational reason for condemning it. You can talk about recessive genes all you want--but the same argument applies to unrelated couples who have recessive genes in common, like sickle cell trait. We don't ban them getting married, even if we do endorse some sort of measure to look out for the potential offspring.
I've seen advocates of gay marriage bristle when consensual adult incest is mentioned, but that makes sense for purely tactical reasons: it does invite other "slippery slope" comparisons; and more importantly, it forces one to confront additional types of bigotry, fighting a two-fronted war. I get that. But "eliminating societal restrictions that are based purely on bigotry" is a kind of slippery slope: if we start confronting our bigotries, there are several others that will inevitably come into the crosshairs as well.
There's a part of this comment that I strongly agree with--and a part that I disagree with.

Here's what I agree with: Any time you argue that a particular social taboo should be set aside because it is based on nothing but prejudice or bigotry, you open the door to the question, "What else is based on nothing but prejudice or bigotry?" Chances are, there are more things than what you've targeted.

In the arena of marriage, forms of intimacy that are currently taboo are numerous, and our social policies on marriage reflect these taboos. As one begins to doubt the legitimacy and defensibility of one taboo, this leads inevitably to the question of whether there are other restrictions on marriage that are rooted in nothing but bigoted taboos.

But questions aren't answers. Questioning the justifiability of taboos against, say, sibling intimacy isn't the same as saying there is no good justification for them.

John Kronen, my friend and co-author of God's Final Victory, encouraged me recently to look at what the 19th Century German philosopher, Hermann Lotze, has to say about marriage in his Outlines of Practical Philosophy. What he says is interesting.

Lotze makes the general point that what the state does, in extending legal standing to an intimate partnership, is to recognize the relationship and "protect the rights of what is recognized." And while the state may withhold such recognition from a particular relationship because the relationship does not reflect "the moral spirit which it wishes to maintain in power in its own midst," he insists that "society has no right to execute punishment upon forms of conduct which merely contract its ways of looking at things, and which have not as yet gone so far as to work positive harm to it."

There's an important distinction here between (a) the state letting relationships form without intervention in individual liberty, and (b) officially recognizing and protecting relationships. Civil marriage is about the latter. Lotze's point is that the state can withhold recognition from relationships for reasons that are more modest than those that would be required in order to prohibit those same relationships.

This seems right to me, and it is important to keep this in mind--but with a crucial qualifier. Withholding recognition is withholding a social good. And any time a social good is made legally available, the decision to withhold it in a given case must reflect a robust respect for the principle of equal treatment under the law. Hence, we need to distinguish between two types of cases: (i) cases in which withholding recognition from a certain kind of relationship entails that a class of individuals are systematically deprived of the opportunity to enjoy the sort of social good that civil marriage confers; (ii) cases in which withholding recognition from a certain kind of relationship does not entail such systematic exclusion. The burden of justification is much heavier in cases of type (i) than it would be in cases of type (ii). In fact, I would be inclined to say that in cases of type (i), the justification for withholding recognition must be comparable in weightiness to what would be required in order to legally prohibit a kind of relationship.

In my two posts on slippery slopes, I've argued in effect that same-sex marriage restrictions are of type (i), and that restrictions against group marriage are of type (ii). But what about sibling marriages? These appear to be of type (ii) as well, since it would be pretty preposterous to presume there was a siblings-only sexual orientation (a sexuality such that one can only sustain sexual and romantic intimacy with siblings and is incapable of working up sexual or romantic feelings for anyone who doesn't share 50% of one's DNA).

This means that the state's burden of justification for withholding legal recognition from siblings is going to be considerably more modest than what would be required for withholding legal recognition from same-sex relationships (which effectively bars all gays and lesbians as a class from access to the social good that civil marriage makes available to others). Social bias alone wouldn't be enough to justify it, but is bias the only reason for the state to withhold civil marriage from siblings?

Lotze actually mentions "marriage between brothers and sisters and very near relatives." He thinks the state has can legitimately withhold recognition of such relationships. Why? Here's what he says:
...not because it contradicts any (not demonstrable) "command of nature," but because a correct moral insight condemns the admixture of different moral relations, each of which can unfold its peculiar beauty and worth only when it does so purely for its own sake.
Lotze does not elaborate or explain what he means, but the passage is a pregnant one. The idea seems to be this: There are different ways for human beings to relate to one another, and each of these different species of relationship has its own "peculiar beauty and worth." The sibling relationship has a potential to be a distinctive kind of beautiful and valuable relationship, but only if it is clearly distinguished from relationships of the sexual/romantic variety. Likewise, the idea seems to be as well that the distinctive good that is realized in the best sexual/romantic relationship may be compromised if it is "admixed" with the form of relatedness distinctive of siblings.

To defend this line of thought, one would need to explore more deeply the kinds of virtues that the best sibling relationships embody...and then examine with care whether adding sexual intimacy to a sibling relationship is in danger of compromising these distinctive virtues. Lotze doesn't do this work, but it's a project worth pursuing...and when I reflect on my relationship with my sister, I find Lotze's claim intuitively right. My sister and I couldn't be for each other what we in fact are for each other were we trying to be for each other what spouses are. And there is something really worthwhile in the former.

Now there's also the matter of whether the state has an interest in "protecting" the sibling species of relatedness against things that might compromise its fullest blossoming; and if so, whether this interest is compelling enough to refrain from officially recognizing incestuous sibling couples in the same way that it recognizes non-incestuous couples when it confers civil marriages on them. It might not be compelling enough if withholding such status resulted in legal discrimination against a class of individuals. But that's not the issue here. It probably would not be compelling enough to justify criminally prosecuting incestuous sibling couples. But that's not at issue here, either.

While I think that Hermann Lotze is probably on to something here, it would take more work to turn his concerns about maintaining the distinct virtues of different relationship types into a sufficient justification for prohibiting sibling marriages (I think his line of argument is immediately stronger when we move from siblings to parent-child relations, by the way). But there is another consideration with respect to siblings that has some connection with what Lotze says, and which I think may provide a more obvious and forceful case for a practice of withholding civil marriage from siblings who defy incest taboos.

Consider the following: Siblings typically grow up with unprecedented access to one another. If we'd prefer that sexual expression be limited before a certain level of maturity is reached, we'd have a reason to try to limit sexual opportunities among adolescents (especially at those times when they are newly awakening to their sexual feelings). But to impose external limits on sexual opportunities among siblings growing up in the same home would require draconian measures, measures that would in the same stroke also seriously undermine the kind of close relationship that, for example, my sister and I always enjoyed while growing up. Internal constraints against pursuing such opportunities--such as what results from the sort of visceral disgust and unthinkability that a strong taboo against sibling sex helps to inspire--offer a more promising approach.

Maintaining a strong, deeply ingrained taboo--sufficient to make siblings balk at the very idea of sexual exploration with one another--may be the best thing a society can do to discourage siblings from sexual exploration before they are emotionally ready for sex and its consequences. Such a taboo may be the only thing that can do this work while at the same time enabling siblings to form the close sibling (non-sexual) intimacy that characterizes the best sibling relationships. But can such a strong taboo be established and maintained if the state extends marriage to adult siblings who defy that taboo? The kind of powerful taboo required to produce self-policing among adolescent siblings may break down if the state treats sibling-marriage as equivalent to marriages among non-relatives.

Given the comparatively modest burden that the state must meet when it comes to withhold recognition from (as opposed to outlawing) relationship forms that don't discriminate against a class of individuals, this concern about the social value of maintaining incest taboos strikes me as more than sufficient.

Parallel arguments can be made, I think, about civil marriage among other kinds of relatives.

Friday, November 1, 2013

Interview with the New Covenant Group

About a week ago I was interviewed by my former colleague--John Shook--for an episode of "The Place," a production of the New Covenant Group. The New Covenant Group is interested in fostering productive dialogue between the religious and non-religious, and this episode of The Place (which includes several other people piping in with thoughts and ideas) is a contribution to such dialogue.

For those interested in spending more than an hour listening to me babble, the video is embedded below:

Are Other Slippery Slopes Any More Slippery? Same-Sex Marriage and Polyamory

My last post aimed to systematically dismantle the argument, offered far too frequently, that allowing same-sex marriage is a slippery slope towards letting Farmer Joe marry his goat. My objective there was not merely to call this argument absurd, as is usually done by critics, but to explain why.

Several people commented in response that there are other slippery slopes that opponents of same-sex marriage are worried about, and which my last post failed to address. Some even suggested that it seems clear that the reasons for allowing same-sex marriage, if accepted, really would serve as equally good reasons for allowing various forms of group marriages (marriages involving a husband with several wives, a wife with several husbands, or more egalitarian groups which I'm tempted to call "cluster-nups").

So, I'm going to walk through here the case against there being a slippery slope from same-sex marriage to group marriage.

Again, let me begin with the following point about slippery slope arguments. They're not always unsound. It all hinges on the reasons why you would be taking a certain step. If those reasons work as well as reasons for stepping into the mess that the critic is worried about, then the critic has offered a legitimate slippery slope argument against treating those reasons as good ones for taking the initial step. I should point out, however, that a legitimate slippery slope argument is not always decisive. Sometimes the reasons for taking the first step are so compelling, so powerful, that even if we don't like what follows, we would be well-advised to bite the bullet and accept it.

But I don't think we have to even explore that follow-up question with respect to the various same-sex marriage slippery slopes that have been proposed--because they aren't legitimate slippery slopes at all.

To make this point, let me begin by reminding everyone of Michele Bachmann's bad case for the view that restricting marriage to heterosexual pairings is not discriminatory. What does Bachmann say? Here's how I summarized it in an earlier post:
A law that restricts marriage rights to heterosexual couples is not discriminatory at all, because everyone in society has the same rights with respect to marriage that everyone else in society has, namely to marry someone of the opposite sex. No one is excluded from marriage. It's just that everyone in society faces exactly the same constraint on who they can marry. It must be someone of the opposite sex. So: no discrimination, and hence no need to justify the discrimination by appealing to some consideration that could warrant differential treatment.
And here's how I responded to that argument in the same post:
...the argument is premised on the assumption that everyone has the same sexual orientation. If everyone had a homosexual orientation, then a law restricting marriage to heterosexual couples would require that everyone marry someone they have no attraction to, cannot fall in love with, cannot sustain romantic feelings with, etc. Everyone in society would be equally denied access to a deeply valued social good, namely legal recognition and support for their intimate, romantic loving partnerships. No discrimination there--although we might wonder why the state would systematically deny everyone access to this social good... 
If everyone had a heterosexual orientation, then--once again--a law restricting marriage to heterosexual couples would be unproblematic. It would preclude everyone from doing something no one had any interest in doing in any event... 
And, of course, if everyone had a bisexual orientation, then a law restricting marriage to heterosexual couples would put the same limitation on everyone...We might wonder why this constraint should be imposed, but the constraint would not be discriminatory against any individuals... 
But people don't all have the same sexual orientation. And so, legally limiting civil marriage to heterosexual couples means that heterosexuals are afforded access to a distinctive good (having their intimate romatic partnerships recognized and supported by the state) that is denied to those with a homosexual orientation.
In short, restricting marriage to heterosexual pairings discriminates against persons with a homosexual orientation. Were there nobody whose capacity for establishing and maintaining romantic intimacy were limited to members of the same sex, a law restricting marriage to heterosexual couples would not deny to any individual a social good available to others. Same-sex couples would still be denied marriage, such that if bisexuals of the same sex happened to fall in love they'd face legal discrimination as a couple. But since each member of the couple would still have access to the social good in question--just not with each other--the discrimination against the pairing would be easier to justify for reasons less weighty than would be required in order to systematically exclude a class of people from any access to an important social good available to those who aren't of this marginalized class.

The point here is this: Michele Bachmann's case that no legal discrimination is going on might actually work if there were no such thing as a homosexual orientation.

Whatever the details of our reasons for endorsing marriage equality for gays and lesbians, the wrong of legal discrimination is front and center for all of us. And that legal discrimination arises because there is such a thing as a homosexual orientation. (And there is. Really. Deny it at the peril of being the kid at the playground who doesn't want to hear the facts and so plugs up their ears and shouts "Nya nya!" to cover up what others are saying.)

But is there such a thing as, say, a polyamorous orientation--that is, a fixed and unchosen disposition, resistant to change, such that the person is unable to develop or maintain a satisfying romantic relationship with any other single individual, but is able to develop and maintain a romantic relationship only with two or more? Put one attractive mate in the room with them and...nuthin'. Add a second, and the person's sexual interest suddenly comes alive for the pair as a pair. A desire to cultivate romantic intimacy bursts forth, complete with an interest in long conversations, personal sharing, walks on the beach, bicycle rides together on a brisk fall day...but only with the pair as a pair. Take one of them away and the interest vanishes completely.

Sure, lots of people (most? all?) have a sexuality that isn't limited to one person. But that's not the same as what I'm talking about. It's one thing to be sexually interested in both Mary and Martha. It's something else to be incapable of romantic attraction towards Mary or towards Martha unless both Mary and Martha are there with you in the bedroom. It's one thing to be able to form intimate relationships with both Mary and Martha--and to have a strong temptation to form one with Martha even though you already have one with Mary. It's something else to only be capable of forming an intimate relationship with one only on the condition that you are also forming an intimate relation with the other at the same time.

That is the kind of sexual orientation that would need to exist in order for a law restricting marriage to pairs of people (and excluding triples and quads, etc.) to be a law that discriminates against a class of people.

The fact is, while there is enormously good and compelling reason to believe in the existence of a class of people with a stable homosexual orientation, there is absolutely no good reason at all to believe that there is anything like an analogous polyamorous orientation.

Furthermore, there is good reason to suppose that polyamorous groups wouldn't be able to form the kind of relationship that civil marriage exists to cultivate and support and encourage: intimate, stable, and enduring life partnerships. It's hard enough for couples to manage the complexities of interpersonal dynamics. But--as I've pointed out before on this blog (although I can't find where at the moment)--adding a third person to a relationship multiplies those complexities enormously. When you have two people, A and B, there is one relationship to deal with. Add a third person, C, and you now have six relationships: A's relationship to B, B's relationship to C, C's relationship to A, A's relationship to the B-C pair, B's relationship to the A-C pair, and C's relationship to the A-B pair.

Of course, all of us have multiple relationships in our lives, and hence have a range of complications to face. But a life partnership--a mutual commitment to share the challenges of life together, to support one another, to be in each other's corner through the years, to divide the responsibilities of making a home, to make crucial decisions as a team--that sort of relationship involves distinctive kinds of stresses and conflicts, as well as payoffs. A three-person life-partnership faces challenges that exponentially magnify these stresses and conflicts: potential for jealousy, for playing off one partner against the other in a way that creates a kind of hierarchy and privilege, for two teaming up and browbeating the third, for alliances that disempower, etc., etc.

The kind of intimacy, of sharing oneself with a life partner, that is at the heart of the best marriages is made enormously more difficult (if not impossible given the realities of human finitude), in the face of such magnified complications and potential pitfalls.

So, not only is there no polyamorous orientation such that a class of people will be discriminated against if group marriages are disallowed; there is also good reason to wonder whether a threesome (or larger group) can even form the kind of relationship that a marriage is supposed to be, let alone sustain it in the lifelong way that is the ideal of intimate life partnership which the institution of marriage holds up.

The relationships that two people have with one another tend to be different in kind from the relationships had by groups of three or more. And it's hardly obvious that the marital kind of relationship is the sort that can be had by groups of more than two. In fact, it seems pretty obvious that it isn't--so much so that I would think the burden of proof rests with those who would argue otherwise.

If I'm right about that, then there's a second way in which it is not discriminatory for the state to preclude polyamorous marriages: Groups of more than two simply can't have the marital sort of relationship at all, so denying it to them isn't denying them anything at all.

But suppose I'm wrong about that. Suppose there is only the one reason why it is not discriminatory to rule out polyamorous marriages in the way that it is discriminatory to rule out same-sex ones--namely the first one I mentioned, having to do with sexual orientation. That would be enough by itself--but there's more to be said. Even if groups of more than two can manage to achieve the marital kind of relationship, achieving it for a larger group would be a truly monumental task given our human condition. Maybe it could be sustained for a year or two. But marriage as a life-partnership isn't realized by pulling something off for a couple of years. And failed marriages are a matter of social concern.

Since no individuals are being discriminated against (absent a polyamorous orientation), the state's burden for justifying a restriction on the number of people who can participate in a single marriage is substantially lower than would be the case were individuals being subject to discrimination by the restriction. And the fact that such a restriction promotes the stability of the marriage contracts that the state helps to create is, it seems, a sufficient reason for the state to restrict official, state-sanctioned marriage to pairs.

(I imagine that greater stability could be attainable in group marriages if there were a clear hierarchy--where, in lieu of genuine partnership, what one had was one dictator ruling it over a few subserviant helpmates. But I also take it that equitable and egalitarian relations among human beings, including between the sexes, is a good that we have a social interest in pursuing. Maybe one reason why conservatives tend to see a slippery slope to polygamy is precisely because they secretly idealize male patriarchy in which husbands lord it over their wives--and don't see a substantive difference between a husband lording it over one wife or over several. But in that case, the slippery slope exists even in the absence of the state extending marriage to same-sex couples.)

Marriage is a stabilizing force. The gay community would be stabilized by access to marriage--but far more so if same-sex marriage were restricted to pairs than if it were made available to groups. Likewise for heterosexuals. The state is in the marriage business in part for the sake of achieving that stabilizing effect, and as such has a good reason to choose that form which does the best job of promoting the stabilizing outcome. (And let me point out that I said "in part," since in the last post some people seemed not to notice this and took a passing remark about one of the state's purposes for marriage as if it were the whole thing. If you want a fuller picture of my views on why the state is in the marriage business, see here.)

If the state has good reason to promote the stabilizing outcome that marriage makes possible, the state has both a reason to make marriage available to same-sex couples (thereby extending its stabilizing effects into the gay community) and a reason to preclude group marriages. Obviously, then, this case for same-sex marriage is not a slippery slope to group marriage.

In sum: Unlike in the case of same-sex marriage, precluding group marriage does not discriminate legally against a class of individuals. Furthermore, there is good reason to suppose that, unlike in the case of same-sex marriage, precluding group marriage does not discriminate in the sense of denying marriage to sets of people who are equally capable of creating the marital kind of relationship--because sets larger than two aren't equally capable. Finally, while the state's interest in promoting social stability is served by extending marriage to same-sex couples (and harmed by precluding same-sex marriage), the reverse is true for group marriage. Thus, all the main reasons that I offered in my previous post for extending marriage to same-sex couples are reasons that just aren't reasons for extending marriage to groups.

Hence, there is no slippery slope. Not even close. Rather than a downward oil-slicked glass slide between same-sex marriage to group marriage, what we have is a series of brick walls.

Note: I haven't talked here about incestuous marriage--but I think the last two posts make the reasoning process for assessing the merits of a slippery slope argument clear enough, so that anyone can discern for themselves the absurdity of saying there is a slippery slope from same-sex marriage to parent-child or sibling marriages (or pedophelic marriages, etc.). In these cases, ask if there is a sexual orientation that makes precluding this sort of marriage discriminatory against a class of individuals. If no, then you don't have a slippery slope. And ask, furthermore, whether the kind of relationship that would (or at least could) result is the sort that legal marriage is supporting. If no, then you don't have a slippery slope. And ask, furthermore, whether there is a significant state interest by which same-sex marriage and this other kind of marriage would have to be viewed differently. If yes, then you don't have a slippery slope.