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.