Going with my constant assertion that, once an argument becomes completely intractable, it's time to throw out all of the existing arguments on both sides and find some new ones because, clearly, the one's we've got aren't going to get us anywhere, here's another thought on gay marriage.
If all people, regardless of race, gender or class, are equal under the law, then why do women have a right or privilege that men do not, namely, the legal ability to marry a man? Contrawise, why are men granted the right to marry women when women are not allowed to do the same? A number of high court precedents, most notably the landmark Brown v. Board..., have held that the constitution makes no provision for equivalent but separate sets of rights for different classes of citizens. If a single person is granted a right, privilege or ability by act of law then that precise action must be available to all people without regard to extra-legal factors.
Absolutely regardless of any moral issues that are presented by same sex marriage, there can be no legal construct that allows for precisely equal rights for both men and women, ergo, either everyone is allowed to do everything or no one is allowed to do anything.
Personally, I vote for no one but I've already talked about that in some detail.