After some brawl-in-the-schoolyard circling, commenter Pragmatist and I have started up another round of the same-sex marriage dialog on Anchor Rising, thus far in the form of a question and answer exchange. Thinking the exercise worthwhile (and curious to see how far we’ll get with it this time), I considered a post of its own to be justified, beginning with his first question:

… why shouldn’t the state encourage monogamous homosexual relationships? Unless you are prepared to take the position of the president of Iran that homosexuals don’t exist, then aren’t strong, stable, monogamous homosexual relationships better for society than the opposite?

To which I replied:

I’m not opposed to states’ seeking to do so, as long as they structure the new institution of same-sex unions from the ground up, without reference to marriage. (When constitutional amendments have been proposed, I’ve always backed versions that would leave that possibility open.) My reasoning (on the secular/civil side) is that modifying the definition of marriage in order to encompass same-sex relationships will undermine the institution as it exists, thus diminishing the states’ encouragement of stable, monogamous relationships between heterosexual couples (which, after all, have the added consideration that they can produce children with minimal intention).
I’ve long said, by the way, that my calculation might change if the pro-SSM movement took up the cause of tighter divorce laws. No takers from your side, yet.

Response:

Yes, I have heard this argument many times. But I have never heard a convincing unbundling of this amorphous concern: “modifying the definition of marriage in order to encompass same-sex relationships will undermine the institution as it exists.” How? How does encouraging MORE stable relationships undermine the institution? Perhaps the struggle of homosexuals to establish this right despite overwhelming odds should reinforce the importance of the institution for heterosexuals? Maybe heterosexuals should be inspired by the struggle and value what they have already even more?

I’ll start by saying that I do think there’s likely been positive development among heterosexuals as the struggle over same-sex marriage has raged, but not because they are inspired by homosexuals’ striking belief in the institution. Rather, in formulating their own positions on the issue, at least those who don’t take their views directly from the oracles of popular culture are spurred to consider what marriage means to them. What the institution is for, and what that meaning requires of them.
That really is the central question: What is marriage about? Reformulated for use in discussion of public policy, the question is: What is the purpose of the government’s recognition of it? By changing the essence of what marriage is, and what it hopes to accomplish, same-sex marriage would undermine the institution in three interrelated ways:

1. Equal rights abide no arbitrary boundaries. If we enshrine into law the principle that marriage is the recognition of intimate adult relationships, defined according to the proclivities of the individual, all subsequent distinctions are fundamentally arbitrary. Polygamy and adult incestuous relationships will follow. Marriage as the encouragement of a particularly stable form of grouping will become meaningless.
2. We won’t abide the government in our bedrooms. Our culture still has strong presumptions about male-female relationships. Yeah, men and women can be friends, even roommates, but there are boundaries that begin to raise suspicions — notably, living together. For the most part, those suspicions have protected marriage from corruptive arrangements of pure self-interest. The gay rights movement has, to some extent, raised suspicion about platonic same-sex relationships, but were same-sex marriage to become available, I think it likely that heterosexuals would exploit the arrangement for economic reasons. And frankly, I don’t see why they shouldn’t. If the civil impetus for recognizing marriage is to encourage mutual care of independent citizens (allowing various assumptions of trust and rights such as the famous hospital visits), then there’s no reason pairings that don’t involve sex shouldn’t be included, whether they involve friends or relatives.
3. Too many won’t abide their own children. The most important of the consequences of codifying the romantic, mutual-intimacy-centered vision of marriage into the law is the competing vision that it displaces: that marriage is fundamentally a desirable relationship between a man and a woman because their intimacy can result in the birth of children. Our society gives marriage weight in order to create a cultural expectation that will draw those who might be inclined to shirk their responsibility into stable families. If marriage and the potential of procreation aren’t intrinsically linked, then there is less pressure on a man to stick with the mother of his children (or a woman their father) for the family’s benefit, even if fleeting romantic feelings don’t fulfill his (or her) fantasies.