Unfortunately, the marriage “debate” has been heating up. This blog entry from John Scalzi has the most coherent comments on it. I’d already considered the argument, but not the rhetorical stance.
So it’s pretty simple: If you actually want to defend marriage, you have defend all the legal marriages, and that includes the ones with two men in them, and the ones with two women. Otherwise you’re explicitly saying that the government has the right to void any marriage of any couple, so long as two-thirds of the House, Senate and states go along. Who wants to be the first to sign up for that?