Not to get into specifics but my interest in, and knowledge of, American polygamy is based on a very personal experience (now in my past). What most bystanders in the mainstream do not realize is that there exists a large, underground movement of folks - people who are not members of authoritarian religious sects - who feel drawn to this lifestyle. Though a show like Big Love (disclaimer: never watched it) is changing perceptions to some degree.
The only fundamental distinction that exists between the gay expansion of the traditional marriage construct and the polygamous one involves power and privilege.
You're forgetting the other half to that equation; the other two key "P" words: "Practice" and "People".
In "practice", polygamy has historically been despicable, and often conflated with another 'p' word:
philia. Yes, they love marrying these girls off when they're 13. If polygamy has been misrepresented, and there is a subculture that isn't rooted in this sort of grotesque ideology, then it is their responsibility to represent themselves and to illuminate their distinctive culture. Homosexuals and their allies have worked hard to do this.
By "people" I mean numbers. Proportions. I don't think the number of polygamists equals the number of gays. The latter is a more prominent group, and by a huge margin. If you want to talk influence, then talk numbers.
There are many very wealthy and very influential homosexuals operating within American society. The same can in no way be said about polygamists (sure, there are a lot of rich and powerful guys with a wife and multiple mistresses... but they are the LAST guys looking to enter into loving, committed, lifelong, binding, contractual agreements with the girls they bang).
This is, sadly, the way "social change" operates most often in a capitalist society. It's bought by those who own sufficient social and political leverage.
Homosexuals have always been concealed in our ranks, and have always had powerful and privileged members of society. The shift in attitude has largely been one of dialogue and understanding. Gay's didn't "buy" their rights. That's a grossly inaccurate narrative you're imposing on the history of this civil struggle by allusion to some irrelevant socio-political theory. They've won sympathy by presenting themselves as fellow human beings with the same fundamental desires as heterosexuals- the desire to behave and acculture themselves identically, as equals, is only further evidence of the fact.
But this is the (ironic) attitude I find so contemptible in the pro-gay crowd: "I'm not going to say that consenting adults should be denied the right to live a polygamous lifestyle. But, please, do not sully the beautiful and honorable institution of gay marriage by trying to equate it with something as untoward as polygamy."
I agree that from my libertarian point of view on the matter that I do not see a fundamental, humanistic difference that should be recognized by a neutral third party like the state. As long as people are adults, consenting, and free, then I don't care how they choose to engage sexually, or to cohabitate in what effectively functions as family.
