In an essay 10 years ago, I pointed out that it is utterly logical for polygamy rights to follow gay rights. After all, if traditional marriage is defined as the union of (1) two people of (2) opposite gender, and if, as gay marriage advocates insist, the gender requirement is nothing but prejudice, exclusion and an arbitrary denial of one's autonomous choices in love, then the first requirement -- the number restriction (two and only two) -- is a similarly arbitrary, discriminatory and indefensible denial of individual choice...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.
To simplify the logic, take out the complicating factor of gender mixing. Posit a union of, say, three gay women all deeply devoted to each other. On what grounds would gay activists dismiss their union as mere activity rather than authentic love and self-expression? On what grounds do they insist upon the traditional, arbitrary and exclusionary number of two?
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.
The law doesn't assess how much two people love each other. Two persons of opposite sexes can marry for all sorts of reasons. If there were a device that could look into their souls and measure their love, we wouldn't accept the outrageous invasion of privacy it would take for the government to use it. Excluding gay couples from marrying does generate the complaint that society does not sufficiently respect homosexual love, and by harping on this point, proponents of gay marriage activate their opponents who think that's a good thing.
But it's not all about love and who respects what. It's also about economics. And in that dimension, it's easy to distinguish polygamy.
UPDATE: This one has a lot of comments! And then there are the other bloggers writing about it. Eugene Volokh is disagreeing with me, but only because he's misreading me, and if he's misreading me, I've got to expect that misreading is rampant. I've tried to keep the commenters here focused on what I'm actually saying, but I can't rein in everyone who's talking about me. There are 98 comments right now on the Volokh post, and I'm probably not going to read many of them. But let me just say why I think Volokh has misread me. He seems takes that last clause "it's easy to distinguish polygamy" to mean what it literally says ripped out of its context. But 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.