Some members of the Supreme Court agree. Dissenting Chief Justice John Roberts argued that "much of the majority's reasoning would apply with equal force to the claim of a fundamental right to plural marriage." In 1996, Justice Antonin Scalia claimed the court had put itself on the path to upholding the rights of polygamists.
They have a point -- though it does more to highlight the problems with banning plural marriage than it does to discredit same-sex unions. There are, it turns out, parallels between the two. Those similarities are not likely to persuade the justices to strike down the existing bans. But they should make the rest of us reconsider.
Before the gay marriage ruling, there was nothing to prevent gays from living together, having sex and raising children like married straights. There is generally nothing to prevent polyamorous people from doing likewise. If several females want to live and sleep with the same guy, nobody will stop them. It's just that only one of them can legally put a ring on it.
Utah, where polygamy has some fans, chose to make it a crime when a married person "purports to marry another person or cohabits with another person." But in 2013, a federal court said that law violated the right to privacy -- the same rationale the Supreme Court used to strike down sodomy laws.
The case for legalizing polygamy builds on the case for legalizing same-sex marriage. The sexual arrangements may offend some people, but they're not a crime. If they aren't done under legal arrangements, they'll be done without them.
If a man is living, procreating and raising children with two or three women, what do we gain by saying he can't easily formalize his obligations to them? Why not let his housemates gain legal protection?
Conservatives raise the specter of polygamy as though its evils are beyond doubt. But much of their opposition stems from religious objections, appeals to tradition or disgust with sexual tastes they do not share.
Those grounds were not enough to justify banning same-sex marriage -- and in the long run, they are not enough to justify banning polygamy. If conservatives want to make sure plural marriage never comes to pass, they need better reasons.
Some plausible defenses have been heard. One is that polygamous weddings, unlike gay ones, actually harm other people -- by reducing the stock of potential mates, dooming some people to singlehood. Another is that polygamy is associated with sexual abuse of minors. It may also be argued that polygamists, unlike gays, don't warrant constitutional protection because they haven't suffered relentless mistreatment.
Those arguments may be enough to keep the Supreme Court from concluding that the Constitution protects polygamy. But they aren't very convincing as arguments for banning it.
Plural marriage would decrease the supply of marriage partners -- but so do informal polygamous arrangements, which take multiple people out of the dating pool.
Besides, no one is entitled to a preferred quota of possible spouses. Some women don't want to marry anyone but George Clooney. When Amal Alamuddin became his wife, she reduced their supply of suitable partners to zero. Too bad for them.
The abuses often seen in polygamist outposts are real, but they are more likely to flourish when Big Love can be practiced only in secret, and they can be prosecuted on their own. We don't outlaw traditional marriage because Ray Rice slugged his wife.
Polygamists have had their share of persecution, at least when they were numerous enough to alarm their neighbors. Mormons didn't migrate to Utah for the salt water. They did it to escape hatred and violence. In 1838, the governor of Missouri ordered their extermination.
None of these rationales, of course, is likely to convince the court to grant a freedom that few people want and that would produce far more complications than same-sex unions. Public opinion affects the justices, and there is no groundswell of support for plural marriage.
But maybe that's because we haven't given it much thought. Conservatives raise it in the context of same-sex marriage to create fear. They should be careful. If people bother to look at polygamy, they may find it's not so scary.