A few days ago, the Anal Philosopher made the provocative assertion that "no conservative can support gay marriage" (hat tip: PikeSpeak). I sent him an email expressing my surprise that a rigorous thinker (as he appears to be) could make such a categorical statement. Either his definition of conservatism comprises a set of principles, in which case different conservatives holding these same principles may have different life experiences and different assessments of the relevant facts and premises, leading them to different conclusions on this issue, OR his definition of conservatism explicitly precludes support for gay marriage, in which case it is merely tautological, and thus not a very promising basis for any rational discourse on the matter. Alas, this gets dismissed as "wacky".
He compares this to other categorical claims such as "No liberal can support slavery." That's actually an interesting analogy. Certainly today it would be incomprehensible for a liberal to support slavery. However, it is quite possible to imagine an early 19th century liberal -- holding the same principles as liberals of today, but applying them with different premises, and coming to a conclusion in support of slavery as it existed before the Civil War. That historical liberal could well have held the same truths we hold as self-evident, but would have found no inconsistency in not applying them to black slaves any more than to women or children. Slaves, like women and children, were dependents to be looked after, human but not citizens. (I tread on sensitive ground here, so just in case anyone is unclear: I am by no means justifying slavery. But I am explaining how someone at that time could have reasonably been both a liberal and a slave-holder. The liberal principles didn't change, but the understanding of the world changed the premises, and thus the conclusions.)
In the same way, it is perfectly conceivable that two people could both be "conservative", but come to different conclusions about gay marriage (and its legal recognition). Here is a good example. In a follow-up post, the Anal Philosopher quotes Princeton professor Robert P. George: "It is certainly unjust arbitrarily to deny legal marriage to persons who are capable of performing marital acts and entering into the marital relationship." I am in complete agreement with Prof. George on this principle. However, Prof. George (who manages from this auspicious start to reach the wrong conclusion) must disagree with me about the fact that two men or two women are indeed capable of performing marital acts and entering into the marital relationship. (Note that the marital relationship does not depend on a state-granted marriage license. Rather, the relationship stands prior to and independent of the state's acknowledgement of it.)
Certainly, the term "conservative" as it is applied in contemporary American politics refers to an amalgam of neo-cons, theo-cons, libertarians, traditionalists, and more. Certainly there are those from the more libertarian strand of conservatism who have begun to recognize that their principles might impel them to accept gay marriage. (Barry Goldwater and William Safire come to mind.) And Jonathan Rauch, in his book Gay Marriage: Why It Is Good for Gays, Good for Straights, and Good for America, mounts a quintessentially conservative argument for gay marriage. Indeed, it turns out that conservative principles and conservative reasoning can lead one to support gay marriage.