It IS unconstitutional. I don't even see how gay rights is up for discussion. If you believe in the Constitution, which says that everyone is guaranteed the same rights (as you'd be hard-pressed to find an American who disagrees) then believing that gays should be allowed to marry and thus, enjoy the same benefits as straight married couples shouldn't even be a question.
But let's face it, we need to legalize gay marriage IMMEDIATELY because gay men are probably the only men who actually WANT to be married.