Judge Posner's argument against polygamy also works against same-sex marriage

Polygamy has been a hot topic in the aftermath of the Supreme Court's finding a constitutional right to same-sex marriage. Indeed, Chief Justice Roberts argued in his dissent that most of Justice Kennedy's arguments apply just as strongly in favor of a right to plural marriage:

It is striking how much of the majority’s reasoning would apply with equal force to the claim of a fundamental right to plural marriage. If “[t]here is dignity in the bond between two men or two women who seek to marry and in their autonomy to make such profound choices,” why would there be any less dignity in the bond between three people who, in exercising their autonomy, seek to make the profound choice to marry? If a same-sex couple has the constitutional right to marry because their children would otherwise “suffer the stigma of knowing their families are somehow lesser,” why wouldn’t the same reasoning apply to a family of three or more persons raising children? If not having the opportunity to marry “serves to disrespect and subordinate” gay and lesbian couples, why wouldn’t the same “imposition of this disability” serve to disrespect and subordinate people who find fulfillment in polyamorous relationships? 

(citations removed for clarity)

And the argument for a right to plural marriage isn't just a gotcha advanced by bitter conservatives. Leftist blogger Freddie deBoer and left-libertarian blogger Will Wilkinson both jumped on the bandwagon, arguing that there should be a right to plural marriage.

In typically idiosyncratic fashion, Judge Posner has come up with an argument that he thinks dispatches this plural marriage stuff:

[T]he chief justice ... suggests that if gay marriage is allowed, so must be polygamy. He ignores the fact that polygamy imposes real costs, by reducing the number of marriageable women. Suppose a society contains 100 men and 100 women, but the five wealthiest men have a total of 50 wives. That leaves 95 men to compete for only 50 marriageable women.

Posner's argument is that a policy that would create an excess of unmarried men imposes a real cost on society, and therefore is certainly not required. In other words, this is at least a rational basis for a ban on plural marriage.

I see a number of problems with this argument. From a legal perspective, it is essentially frivolous because it has nothing to do with the reasoning of Justice Kennedy's opinion, which is based on liberty and equality, not economics or utilitarianism.

But, more subtly, it could just as easily be used to construct a rational basis for a ban on same-sex marriage, at least if it's plausible that there would be more homosexual women than homosexual men. Consider Posner's society of 100 men and 100 women, but where 6% of the men and 10% of the women are gay. If same-sex marriage is allowed, the 6 gay men and the 10 gay women pair up. That leaves 94 straight men fighting over 90 "marriageable" straight women. We've got four extra, lonely men. This counts as a "real cost" in Judge Posner's world.

And, to the best of my understanding, it is in fact true that women are more likely to identify as LGBT:

The gap is even bigger if you just look at younger people, who have grown up in a society much more tolerant to homosexuality and thus might reasonably be expected to be more honest about, or even aware of, their sexual orientation:

If you do the math, you can construct an argument that permitting same-sex marriage could leave millions of American men with no potential spouse:

1) According to the 2010 census, there were approximately 41.6 million men and 41.3 million women between the ages of 20 and 39. (So you'll notice that we start with a problem.)

2) Using the more extreme figure of 8.3 percent LGBT females and 4.6 percent LGBT males, we are left with 37,872,000 million "marriageable" straight women for 39,686,000 straight men to fight over. That's 1,814,000 extra, "unmarriable" men -- over 4 percent of the prime-age male population!***

Thus, based on Judge Posner's reasoning, we have found the "real costs" of same-sex marriage, and constructed a rational basis to require that marriage remain a one-man, one-woman institution.

Just to be crystal clear, I don't actually think this hocus pocus is a good argument against same-sex marriage. But all the reasons that make it a bad argument against same-sex marriage make it an equally bad argument against plural marriage.

***Totally weird coincidence: there are about 2,000,000 American men in prison right now.