If Krauthammer has been writing about this subject for 10 years, it boggles the mind that the obvious distinction has not yet dawned on him.
Legal marriage isn't just about love, it's an economic arrangement. Having the state authorize your union is not the same thing as having your friends and neighbors approve of you and your religious leaders bless you. It affects taxes and employee benefits — huge amounts of money. A gay person with a pension and a health insurance plan is incapable of extending those benefits to his (or her) partner. He (or she) can't file a joint tax return. That's not fair. A polygamous marriage, however, puts a group of persons in a position to claim more economic benefits than the traditional heterosexual couple. That doesn't appeal to our sense of fairness. . . .
[I]t's not all about love and who respects what. It's also about economics. And in that dimension, it's easy to distinguish polygamy.
I generally much like Prof. Althouse's work, but here I'm unpersuaded. She gives a good argument for not giving polygamous families more benefits than two-member families have. But it's easy to exepct what polygamous families would say in response:
We're not asking for benefits that would extend to all the spouses in the family. All we're asking for is what two-member families get. We want the symbolic value of having our marriages recognized as marriages, which doesn't impose economic costs on anyone. We want other no-cost or very low-cost benefits. And for the costly benefits, such as insurance and pensions, we'll be happy if the law just covers two members of our marriage; we'll take care of the other members on our own.
We don't want coverage for three, four, or five members. We just want coverage for two, just like the rest of you get. But it's unfair if you entirely reject our marriage, and give us coverage only for one.
I've argued in my Same-Sex Marriage and Slippery Slopes that polygamous marriages are indeed unlikely to be recognized in the U.S., even if same-sex marriages are recognized. If the same-sex-marriage-recognition movement wins, and especially if it wins by stressing certain kinds of arguments, those arguments may indeed be logically usable by polygamy-recognition forces. But, as I argued, "It takes more than a plausible argument to win battles like this, either in the legislature or in court. It makes more than a plausible argument plus some slippery slope effects. It takes a broadly supported political and legal movement (whether of a majority or a committed substantial minority) of the sort that gay rights advocates have managed to muster. I doubt that there’ll be such a movement for polygamist rights, even with the potential slippery slope effects I describe."
Nonetheless, though I'm not terribly impressed by the slippery-slope-towards-recognizing-polygamy arguments, I don't think they can be dismissed as easily as Prof. Althouse suggests. It's not enough to come up with a plausible distinction between what one supports and the extreme version of what others support. One also has to deal with the more modest versions that the others will come up with in response to your distinction.
UPDATE: My disagreement with Prof. Althouse may be less than I thought; in an update to her post, she writes:
I'm not saying that the distinction is so obvious that everyone will accept it. I'm just refuting Krauthammer, who thinks there is no way to stop the slip down the slope from gay marriage to polygamy. I'm against the scare tactic that is being widely used: don't accept gay marriage or nothing will stave off polygamy. All I'm saying is that there is a principled basis for drawing a line between the two. Nothing compels us to choose that line, however. I freely admit that.On that, I agree; as I've stressed in all my writing on slippery slopes, it is very rarely the case that the first step will absolutely positively guarantee to lead to the future step (as in "nothing will stave off"). People who overstate the slippery slope argument by making it sound like the bottom of the slope is inevitable end up weakening their own position.
Nonetheless, it still seems to me that a distinction between recognizing same-sex marriage and recognizing polygamous marriage should -- to be practically useful and not just theoretically plausible -- do more than just explain why the most extreme version of recognizing polygamous marriage (recognize my marriage and put all eight of my wives on my insurance plan) is distinguishable from recognition of same-sex marriage. It should also explain why the likely alternatives that you'll be given in response (recognize my marriage and put one of my wives on my insurance plan) is distinguishable.