It's natural for any group to decide upon how it will operate by surveying its members.
I'm thinking more and more that it's only big groups (150ish+) that really need a formal system of voting, though.
http://en.wikipedia.org/wiki/Dunbar's_number
Small groups, in which everybody knows everybody, lives and works and regularly hangs out with everybody, seemingly have less need to officially decide on rights issues.
Incidentally, I've seen anti-gay people in my own life do a 180 when they learned that someone close to them was gay. Suddenly gay people weren't other or they. This happened with my ex-mother-in-law when she learned that a young man she babysat and knew his whole life came out of the closet.
Most people against gay marriage that I know really don't have gay friends or spend any real amount of time with gay people (outside work or whatever). I mean, really hang out with them, vacation with them, drink with them, meet their family, etc.
Dunbar's Number says that a person, on average, is able to have about 150 stable, active relationships. I'd say that inside my 150, easily 75 or more are friendships with gay people (which includes familial relationships). So in my microcosm, gay people aren't a minority at all and the idea of them having second-class citizen rights is insane.
As far as human/civil rights are concerned, and which should be voted on...
I say if a person is a law-abiding, tax-paying citizen of a society, then they should have any and all privileges that the society confers. The recognition of social monogamy (marriage) is one of those privileges and so are the health and tax benefits, etc. that come with it.
I really don't see how it gets more complicated than that.
The only case in which I think a person should be denied the privileges of her society is if she breaks a serious law or isn't paying her dues.
I guess I will throw in that I think any person paying taxes (including 15 and 16 year olds) should have the right to vote. It's awful that they're expected to pay into the system but have no voice in it.