Over at the libertarian Volokh Conspiracy, Ilya Somin finds arguments against same-sex marriage to be insufficient. If you ban same-sex marriage on grounds of poor outcomes, then why not ban other marriages with similar outcomes? (Sexual orientation alone isn't sufficiently impressive.)
The post is worth reading at length. The comments, are, too, particularly this exchange.

Gays and lesbians are only about 3-4 percent of the population, according to most surveys, and few heterosexuals look upon them as role models for how to manage their own marriages and sexual relationships. Even if we assume that most gay and lesbian marriages will set a poor example for heterosexuals, by e.g., promoting the idea that promiscuity is unobjectionable, or by being bad parents to their children, there is no reason to believe that heterosexuals will actually follow that example. If we assume, more realistically, that at worst same-sex marriages will be on average moderately worse than the heterosexual ones, but there will be great variation within each group, then the likelihood of a negative influence is even smaller. Even if you believe that raising children is the only good justification for marriage, many gays and lesbians are in fact raising children, and get married in large part for that reason. Most heterosexuals who don’t follow the subject closely probably won’t even know the data on the relative quality of same-sex marriages, much less model their own behavior on it. I don’t mean to suggest that same-sex marriages really are, on average, worse than heterosexual ones. But even if that is in fact the case, it is unlikely that heterosexual marriage will be much affected as a result.
In practice, the existence of gay marriage is likely to have only a very modest effect on the vast majority of heterosexuals. Because it involves such a small group, the introduction of gay marriage is actually a far less consequential social change than the legalization of interfaith marriage and interracial marriage, and the replacement of traditional patriarchal marriage that concentrated legal authority in the hands of the husband with a system where men and women have equal rights. Each of these were much more radical changes that affected large parts of society.
But if we nonetheless believe that the possibility of negative example effects is a good reason to ban same-sex marriage, it’s an even better reason to ban the much larger number of heterosexual marriages that involve people who are statistically likely to set a poor example for others. Such factors as poverty, low intelligence, a history of criminal behavior, and so forth are all highly correlated with social dysfunction within marriage, such as promiscuity and child and spousal abuse. And the number of heterosexuals who fall into these categories is far larger than the number of gays and lesbians. Dysfunctional heterosexual marriages are far more likely to have a negative effect on social mores than dysfunctional same-sex marriages. Yet almost no one claims that we should therefore ban poor people, people with low intelligence, or even criminals from getting married.
The post is worth reading at length. The comments, are, too, particularly this exchange.
