I still don't see how this differentiates it from normal marriage, which is another overpriced parade to attempt to conform to a wholly unnecessary societal norm.
Also, we need to consider two forms of marriage: ceremonial and legal. I'm advocating that legally, people should have the rights to marry regardless of who they are as long as both can consent. This is because the government has no place in determining who lives, sleeps, etc, with who, therefore we should give them the full range of legal options to sort out how they do that. As for the ceremonies, again it should just be left up to individual groups to decide what they want to sing, dance, or make long droning speeches about.