Jonathan Rauch is a senior fellow at the Brookings Institution and author of Gay Marriage: Why It Is Good for Gays, Good for Straights, and Good for America.

I am a gay marriage advocate. So why do I spend so much of my time arguing about polygamy? Opposing the legalization of plural marriage should not be my burden, because gay marriage and polygamy are opposites, not equivalents. By allowing high-status men to hoard wives at the expense of lower-status men, polygamy withdraws the opportunity to marry from people who now have it; same-sex marriage, by contrast, extends the opportunity to marry to people who now lack it. One of these things, as they say on Sesame Street, is not like the other.

Yet this non sequitur just won't go away: "Once we stop limiting marriage to male-plus-female, we'll have to stop limiting it at all! Why only two? Why not three or four? Why not marriage to your brother? Or your dog? Or a toaster?" If there's a bloody shirt to wave in the gay-marriage debate, this is it.


The shortest answer is in some ways the best: Please stop changing the subject! When you straights give yourselves the right to marry two people or your brother or your dog or a toaster, we gay people should get that right, too. Until then, kindly be serious.

If I sound exasperated, it's because the polygamy argument doesn't stand up to scrutiny. That doesn't stop it from popping up everywhere. A good example of the species can be found in this publication, where Fredrik deBoer welcomed Politico Magazine's readers "to the exciting new world of the slippery slope."

"Now that we’ve defined that love and devotion and family isn’t [ sic] driven by gender alone, why should it be limited to just two individuals?” he asked. “The moral reasoning behind society’s rejection of polygamy remains just as uncomfortable and legally weak as same-sex marriage opposition was until recently."

The assumptions here seem to be two. Point 1: If there’s no good reason to oppose same-sex marriage, then there’s no good reason to oppose polygamy. Point 2: The Supreme Court ruled in Obergefell v. Hodges that gay marriage is a fundamental right, so polygamy must also be a fundamental right.

In his dissent in Obergefell, the ordinarily astute Chief Justice John Roberts goes in for this logic. Point 1: The majority, he says, "offers no reason at all why the two-person element of the core definition of marriage may be preserved while the man-woman element may not"—implying that, because the majority offered no rationale against polygamy (in a case that was not about polygamy), none exists. Point 2: "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." And so, says Roberts: "There may well be relevant differences that compel different legal analysis. But if there are, petitioners have not pointed to any."

No relevant differences? Let's help him with that.

Unlike gay marriage, polygamy is not a new idea. It's a standard form of marriage, dating back, of course, to Biblical times and before, and anthropologists say that 85 percent of human societies have permitted it. This means we know a thing or two about it.

Here's the problem with it: when a high-status man takes two wives (and one man taking many wives, or polygyny, is almost invariably the real-world pattern), a lower-status man gets no wife. If the high-status man takes three wives, two lower-status men get no wives. And so on.

This competitive, zero-sum dynamic sets off a competition among high-status men to hoard marriage opportunities, which leaves lower-status men out in the cold. Those men, denied access to life's most stabilizing and civilizing institution, are unfairly disadvantaged and often turn to behaviors like crime and violence. The situation is not good for women, either, because it places them in competition with other wives and can reduce them all to satellites of the man.

I'm not just making this up. There's an extensive literature on polygamy.

Here’s a 2012 study, for example, that discovered “significantly higher levels of rape, kidnapping, murder, assault robbery and fraud in polygynous cultures.” According to the research, “monogamy's main cultural evolutionary advantage over polygyny is the more egalitarian distribution of women, which reduces male competition and social problems.”

The study found that monogamous marriage “results in significant improvements in child welfare, including lower rates of child neglect, abuse, accidental death, homicide and intra-household conflict.” And: “by shifting male efforts from seeking wives to paternal investment, institutionalized monogamy increases long-term planning, economic productivity, savings and child investment.”

There’s more, but you get the idea.

In this article, I noted other research suggesting that societies become inherently unstable when effective sex ratios reach something like 120 males to 100 females, such that a sixth of men are surplus commodities in the marriage market. That's not a big number: "The United States as a whole would reach that ratio if, for example, 5 percent of men took two wives, 3 percent took three wives, and 2 percent took four wives—numbers that are quite imaginable, if polygamy were legal for a while."

By abolishing polygamy as a legal form of marriage, western societies took a step without which modern liberal democracy and egalitarian social structures might have been impossible: they democratized the opportunity to marry. It's no coincidence that almost no liberal democracy allows polygamy. Here's the map:

Source: Wikimedia Commons

With all due respect to the Chief Justice, if reducing rather than expanding marriage opportunity and destabilizing rather than stabilizing society aren’t “relevant differences” between polygamy and same-sex marriage, I don’t know what would be.

Now, people who want to take issue with the theoretical and empirical literature on polygamy should feel free to do so. What they should not do is what Chief Justice Roberts and Fredrik deBoer do, which is to ignore the literature altogether. Blandly asserting that there's no good reason to oppose polygamy once gay couples can marry makes no more sense than saying there's no reason to oppose date rape or securities fraud once gay couples can marry. It doesn't follow, and it isn't true, and the intellectual laziness implicit in asserting it is epic.

Next, a point of law: In order to stand up in court, a challenged law normally needs only to survive what's called a rational-basis test. That's a low bar: the government merely needs to be able to claim that its law is rationally related to a legitimate government purpose.

The trouble that gay-marriage opponents kept running into was that they could not surmount this very low bar, because they couldn't explain how preventing gay couples from marrying served any of the state's claimed goals. Nor could they show any plausible harm from gay marriage. Justice Anthony Kennedy's opinion for the majority in Obergefell makes this point explicitly: "With respect to this asserted basis for excluding same-sex couples from the right to marry, it is appropriate to observe these cases involve only the rights of two consenting adults whose marriages would pose no risk of harm to themselves or third parties."

Here again, the situation with polygamy is diametrically different. There is ample evidence that polygamy has many severe consequences for third parties and for society as a whole, and the social interests at stake are very obviously related to a legitimate government purpose (many purposes, in fact). There's no way the ban on polygamy could fail a rational-basis test.

Ah, but what if rational-basis isn't the standard the courts apply? What if they find that polygamy implicates a fundamental right? In that case, "strict scrutiny" would normally apply. That's a higher bar: the law under challenge must further a "compelling government interest" and must be narrowly tailored to achieve its goal.

The ban on polygamous marriage quite easily passes this test, too. The government's interest is as compelling as they come, and the policy is tailored quite appropriately to fit the goal. Remember: it's legal for a man to live with multiple women, have sex with multiple women, and even raise children with multiple women (or men!). All the government is doing is denying plural relationships the specific government benefit of a marriage license. This is a well-tailored way to prefer and institutionalize monogamy, without making private consensual conduct illegal.

It also avoids forcing the government to redefine marital relationships in all kinds of ways, because there is no existing template for polygamy. Think about it. Does a polygamous license marry all the wives in a polygynous combination to each other, or each separately to the man? Among multiple spouses, who has primacy in medical decision-making? When kids are born into multiples, do all spouses get some form of parenting rights? How would divorce and alimony work?

Allowing same-sex couples to marry requires only small institutional and legal adjustments (like revising gendered language on some documents). In sharp distinction, polygamy requires making a host of contentious social and legal decisions to rewire marital arrangements pretty much from scratch.

There might conceivably (although not likely) be a case for taking the trouble to do all that messy and confusing rewiring if the moral claim of polygamy were remotely as strong as to the moral claim of gay marriage. But it is not. Gay-marriage advocates have never demanded the right to marry everyone (multiple partners), or anyone (our parents), or anything (our dog or a toaster). We demanded the right to marry someone, as opposed to no one. Unless we were prepared to fool ourselves or a person of the opposite sex, our marriage opportunities were the null set. We were excluded, and it was this exclusion that denied a fundamental right.

Justice Kennedy's opinion understands this. "Marriage responds to the universal fear that a lonely person might call out only to find no one there," Kennedy writes (italics mine). To be sure, he rests his analysis partly on an interracial-marriage case that did not involve a total exclusion, but he takes care not to stop there. "Their hope," he says of same-sex couples, in his final peroration, "is not to be condemned to live in loneliness, excluded from one of civilization’s oldest institutions." (Italics mine.)

Yet again, polygamy is very different. Would-be polygamists are not constituted to be capable of loving only groups rather than individuals. Like most people, they can love multiple individuals, but, unlike most people, they want the supplementary option of marrying them all. Their hardship is hardly comparable to exclusion from the institution of marriage; and likening the two claims is as much of a non sequitur as saying that if women get the right to cast one vote, men should have the right to cast two.

So, when the fundamental right at issue in gay marriage is properly understood as the right not to be excluded from marriage, the polygamist claim is not fundamental. I'm sure that won't stop polygamists and polyamorists from filing lawsuits claiming that the law impermissibly excludes their preferred type of marriage, and that there's a fundamental right for every type of marriage to be available, and that polygamy is a wonderful thing, and so on. But their case is trivially easy to distinguish from Obergefell, which was based on a very different kind of moral, social, and legal proposition.

Indeed, the two cases are not merely distinguishable: they are antithetical. The principle on which gay marriage won social and judicial approval—the principle that individuals and society are better off when everyone has the opportunity to marry—militates against polygamy, not for it. I think the public and the courts will have the sense to see as much—as will Chief Justice Roberts, when he gets around to thinking a little harder about it.