Sullivan articulates a crucial distinction that I think gets lost in the shuffle:
Gay people are not asking for the right to marry anybody. We’re asking for the right to marry somebody. Right now, heterosexual polygamists have an option: marry someone. And gay people are told: you can marry no one at all. That cannot be just. It cannot be fair. And it cannot be conservative to refuse to give 9 million people an incentive to settle down and take care of one another.
His premise is that sexual orientation isn’t a choice, but polygamy is. That’ll be an interesting debate, but I think he’s correct. Among the goods of marriage (Augustine scholars, review your notes) are the reigning in of sexual appetites within a healthy sphere (that is, with a consentual spouse) in a way that deepens and strengthens the bonds of the union. One of the evils of breaking the marriage covenant (through adultery, say) is the weakening of those bonds. One can choose adultery, or fidelity. One can choose to give oneself entirely to a life-long partner, or not. And in a similar way, one can choose, I gather, to try to do that with muliple partners (the previous problems of polygamy to be noted). The point that conscious choice is involved. One isn’t choosing the orientation to a particular sex (though certainly how one acts that out is chosen), nor the fundamental desire to be united with someone (for all the goods of a marriage or other committed relationship). Those are more or less innate.
So a good case could be made for that distinction. Good argument. Go read it….