As Brock notes below, the gay marriage debate has spawned some odd threads, including a discussion of the constitutionality of non-procreative marriage by Jacob Levy. While, in general, I’m not particularly interested in this debate*, I think there are a couple of plausible interpretations of the constitutionality of marriage:

• A textualist argument would say the Constitution has nothing to say on the issue, either way; marriage is not explicitly mentioned in the Constitution. Pure strict constructionalism would argue that this gives Congress no right to legislate on marriage, as that is not an enumerated power of Congress. An expansive reading of the “necessary and proper” clause would argue that Congress can regulate marriage, at least between residents of different states (under the interstate commerce clause), or in all circumstances, as marriage may be part of the “general welfare.” Neither interpretation seems to suggest that marriage would be a constitutional right, though.
• An originalist argument would say that the Constitution is only construed to protect marriages that were permitted under English common law at the time of independence (under the meaning of “liberty” at the time). This would probably limit constitutionally protected marriage to marriages involving one man and one woman, within a single race, and instituted by a religious ceremony of some form. Clearly, an originalist argument would no longer be supported by precedent, as interracial marriage is constitutionally protected (see Loving v. Virginia) and so, presumably, are civil marriages.
• An argument based on the majority holding in Lawrence v. Texas would probably consider marriage as a constitutionally protected “liberty interest” absent a compelling state interest to the contrary. This would place the burden on the state to show there is an overwhelming interest that isn’t based on prejudice against gay marriage, something that I think would be very hard to show.

There’s also a second argument surrounding gay marriage: whether the “full faith and credit” clause requires states where certain marriages are not constitutionally protected to acknowledge those marriages if they were conducted under the laws of another state (say, Massachussetts). Absent a clear textual command to the contrary, I, like Matt Stinson, suspect you could find at least some state or federal courts that would say “yes,” although I don’t think the U.S. Supreme Court would eventually concur. However, some state supreme courts probably would.

What worries me is that, like abortion, this will become one of those interminable debates that paralyzes the judiciary—and by extension, politics at large—because the Supreme Court takes sides too soon in the wider political debate. The last thing this country needs is another “culture war” where the Supreme Court has essentially placed a highly controversial issue beyond ordinary politics. It’s the sort of thing that leads to both parties taking absurdly extreme positions and is ripe fodder for demagoguery by the likes of Roy Moore and the Buchananites.