Random late-night browsing whilst procrastinating w.r.t. proofreading a camera-ready copy of a paper: as a thought experiment Belle Waring constructs an intellectually non-ridiculous argument against same-sex marriage; and (linked from the above comment thread) a plea for intellectual humility from Jane Galt, of all people, that's also not entirely ridiculous.
I have two reactions. First, any intellectually honest person who opposes same-sex marriage for the linked reasons should also support denial of marriage benefits to childless heterosexual couples. But opponents of same-sex marriage won't come out against childless heterosexual couples. Why not? Because society views childless heterosexuals (unlike homosexuals) as first-class citizens, and therefore, it would be incredibly unpopular to infringe on the autonomy of heterosexuals. People believe that heterosexual couples have a right to choose both marriage and childlessness for themselves. Besides, some childless heterosexual couples are childless for painful personal reasons; adding insult to injury by denying them marriage benefits seems beyond the pale. I could say closely analogous things for committed homosexual couples --- that they have the right to choose marriage, and that denying them benefits is cruel --- but the anti-same-sex-marriage forces wouldn't care. Therefore, let's admit the role that power, stemming from bigotry, plays in the acceptance of even the relatively respectable arguments proposed by Galt and Waring: although we would not treat heterosexuals this way, we will treat homosexuals this way, because it is popular to do so, and therefore we have the power to do so.
Second, on a somewhat different track, I want to make a larger point, which is that sometimes the well-being of society simply must defer to individual rights. Individuals are ends-in-themselves, whereas society is a means to furthering the ends of individuals. If guaranteeing individual rights commensurate with our values ultimately leads to the breakdown of society, then so be it.
It is conceivable that a society built upon individual autonomy, civil liberties, and equality before the law cannot be sustained indefinitely. It is conceivable that on the grand scale of history, each era when such institutions prevail is a brief interlude, like foam on the crest of a wave, which inherently rises and then subsides, whereas discrimination and oppression are a sturdy bedrock which endures. It is conceivable that the American experiment in constructing ever-widening circles of social equality contains the structural causes of its own collapse, and that it will therefore recede and be replaced by something more morally repugnant and more sustainable.
So what? Happiness is always finite, but at least it is happiness. Most love affairs contain within them the seeds of their own destruction, but this does not compel us not to love. If equality before the law cannot endure forever, then at least we're lucky enough to have lived in a time when it prevailed. Maybe in some distant future, after same-sex marriage and America's million other concessions to the pursuit of individual happiness have destroyed America, and some dark millennia have passed without us, some other people will, for a fleeting few centuries, be lucky enough to live in such an era again. If so, then I hope that they, too, refuse to destroy their happiness in order to save it.