Recently, my favorite conservative, Bogart, asked me about the legal challenges to anti-polygamy laws using the precedents from the gay marriage debate to argue that government has no right to prohibit the actions of consenting adults. I have a distinct impression that Bogart was trying to bait me into saying that either (a) the precedents such as Lawrence v. Texas were wrong; or (b) that polygamy is all good. The thing is, same sex marriage and polygamy are two different things. When states allow same sex marriage, the following happens:
Polygamy is a completely different animal. For one, plural generally occurs when there is a distinct power imbalance between the sexes. Indeed, plural marriage would necessitate that one gender is dominant. If I had three wives, I could afford to piss off two of them at any one time, and be fine. And if I managed to piss off all of my wives, I could just as easily find a new wife. This is why cultures that allow plural marriage tend to have an extreme inequality between the sexes. For this reason alone, plural marriage would violate the governmental policy of equality between the sexes.
Now, a way to avoid the inequality, of course, would be to allow my hypothetical wives to marry other men while being married to me. But ultimately, this leads to the other problem with plural marriage - it would require states to redefine marriage. Now, this argument has been made about same sex marriage, but in the case of same-sex marriage, the only difference between same-sex marriage, and opposite sex marriage without traditional gender roles is who is getting married, and maybe the sexual practices of the participants in that marriage. That's not a good reason to ban same-sex marriage.
Plural marriage would necessitate the rewriting of the family law statutes because all marriages come to an end - either by divorce or death. What happens then? If one of my hypothetical wives divorces me because I'm being a dick, or because she likes her other husband more, how is the marital estate divvied up? Or, if the State deems me and my wives married to one another, what happens if one of my hypothetical wives divorces one of my other wives? The whole concept of the marital estate would have to end.
And ultimately, that's reason enough to not legalize plural marriage. Marriage from a government's perspective is all about property. Not love, not commitment, not children, but property. Two people want to become one in the eyes of the government, fine, then they're property is as of one. Throw that out, and there is no reason for government to even acknowledge marriage. So yes, people should be able to live their lives as they want, and certainly decriminalization of plural marriage isn't a bad idea, but the legal recognition of plural marriage is simply too problematic to allow.
*I'm referring, of course to the Rational Basis Test where Courts will allow minor intrusions into due process or equal protection rights for even the most half-assed reasons. If you have the chance to read Judge Walker's decision, please do so. The arguments in favor of Prop. 8 all fell into "gay people are bad, m'kay," category.