While I'm fine with polygamy, polyandry, all forms of polyamory, I am decidedly against government recognition of such.

My main reason would be divorce. There is a very high divorce rate in the US today, and a lot of regulation and legal precedent surrounding the terms of and division of property within a divorce, as well as things like alimony, child support, the whole 9 yards.

A marriage with more than 2 partners, when seeking a partial or complete divorce, significantly muddies the waters here. Even cases with 2 partners that would appear to be simply cut and dry are not.

Say, there are 4 people in a relationship. Genders don't matter. Now, for whatever reason, 3 of them want the other one gone. Maybe s/he was unfaithful, maybe s/he was simply lying, whatever. Even assuming no or shared fault, and no other special considerations such as children, shared debt, etc- how does this work out? Does the person leaving the relationship receive 1/4 of the overall value of the shared property? Are the remaining 3 required to jointly provide an alimony equivalent to sustain the fourths lifestyle?

And what if it's more complicated than that? What if this relationship has two men, two women, and both women have children fathered by both men? What if, What if, What if? The only ones who win are the damned lawyers.

If a group of people can make a polyamorous relationship work, then I applaud them, and I consider what they've achieved to be quite beautiful, in a way that a normal marriage simply can't be. But I don't think the government needs to get any kind of hook into this. Really, the government needs to get the hell out of monogamous marriage as well- gay or straight.