this might be a bit more intellectual for the "legalizing gay marriage is assimilationist" crowd, but what about looking at the dialectics of the situation?

The right wing constantly argues that marriage is an unchanging institution, when both history and the struggle for gay marriage show that it is not.

We mock the right-wingers when they say that gay marriage will destroy hetero marriage. For sure, what does a gay couple being together have anything to do with a straight couples problems? But in a certain sense, they are right, marriage as it once was, is no more.

We should support legalizing gay marriage as a dialectical step towards the abolition of all state/capitalist intervention in sexuality.