Whenever you get involved with talking about rights, you're talking about being a citizen. You're talking about being a citizen in capitalism; you're talking about what rights are granted to what identities, under what laws, and all that is a big mix. Marriage is, among many other things, a formality to channel capital through a family. And that's why the big DOMA lawsuit was about paying too many taxes! "I wouldn't have had to pay all these taxes if Theodora had been Theo" - that was the big tagline. It's all about protecting assets.
