The Supreme Court's landmark decision that same-sex marriage is a constitutional right brought out an avalanche of commentary about the possibility of polygamy. Indeed, a Montana threesome is already suing for the right to marry.

This shouldn't be surprising. But what is surprising is just how weak the arguments against legal polygamy are. They rely on class and religious prejudices, as well as on rationales that were deemed illegitimate when launched at same-sex couples.

Jonathan Rauch, who did more than almost anyone else to mainstream the cause of same-sex marriage, finds the argument for polygamy an unfortunate distraction. Rauch's main argument is that polygamy will hurt the ability of low-status men to marry, thereby limiting marriage opportunities rather than broadening them:

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. [Politico]

Rauch is blurring two meanings of the word opportunity. One concerns a legal matter, and the other a social barrier. Rauch equates the "right to marry" with "the right to somewhat equitable marriage prospects," which are different things. Instead of a right to marry the person you want regardless of whether you are both of the same sex, Rauch posits the idea of a government that regulates a market in spouses to make it more congenial to the men with the worst prospects.

Rauch is on logical thin ice when he says that legal polygamy will withdraw opportunities for marriage. He writes, "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." In fact, it could be stated the opposite way. Laws against polygamy exclude the possibility of women marrying high-status men just because they are married, pushing those women toward marriages with marginal low-status men, which present trends tell us they do not want.

The truth is that a plaintiff who wants to be the third wife of Brad Pitt does not have her marriage prospects meaningfully expanded by monogamous marriage laws. "No, your love cannot be recognized by the state, in the interests of jobless schlubs," the judge would say, if he's following Rauch's line of reasoning. And if you think about it, laws making space for polygamy would offer a dramatic increase in the number of possible marriages.

Rauch also says that polygamous marriages do not grow out of an innate quality like heterosexuality or homosexuality. Does he not realize that this reads the "B" out of LGBT? It implies that bisexual identity is unworthy of expressing itself in concurrent loving relationships recognized by the state. Also, there are religious groups in this country that do sanction polygamy. Is he for denying their free exercise of religion?

What's most surprising is that Rauch does not recognize how much he recycles the arguments of same-sex marriage opponents in his own arguments against polygamy. He cites studies showing increased social disorder among polygamous groups. When aimed at gay men's promiscuity or suicide rates, these studies were dismissed by Rauch and others as evidence of legal and social discrimination, not of some inherent immorality or dysfunction.

In this way, he becomes like the recent immigrant who argues for closing the border. Sorry, consent is the measure for me. Discrimination for thee.

David Frum joins Rauch in arguing that polygamy is banned because it is associated with patriarchy and abuse. But the historical reality is that polygamy was banned for the same reason same-sex marriage was: It was unthinkable because of the marriage norms established by Christian civilization. When polygamy was last challenged in the American legal system by Mormons in the 19th century, it was not criticized by the public as the site of nasty traditionalism and pederasty, but as libidinous, and a violation of what everyone took to be decent Christian living. Mormons were widely thought to have engaged in bacchanals, what moderns call sex parties.

Frum and Rauch should have more faith that our nation can Americanize these institutions. Just as modern American same-sex marriage looks different than "Greek love" did to the ancients, so too will American polygamy be more egalitarian than what you find in Somalia.

The Mormon response then was instructive for today's polygamists. They said polygamy was pro-women. They pointed to the relatively better position of widows in Deseret, who often remarried into large families where they received social and economic support. Polygamy was flexible. Mormon wives didn't all live fearfully in sheltered rooms like Branch Davidians. Some brides in plural marriages continued to live with and support their parents. Some of Brigham Young's wives were widows or orphans who were guaranteed a social place by their connection to him.

Instead of considering polygamy a slide into ancient barbarism, a new movement for polygamy will inevitably portray itself as pro-women. Some women will claim that it frees them from the doom of being some schlub's one-and-only. Others may find it frees them from trying to become "everything" to the demands of a high-status partner. Some may enjoy both of those freedoms at once. And does anyone believe today's "high-status males" are more likely to be wife-beaters than jobless males?

What Rauch is ultimately arguing is that bourgeois society is superior to the furies of unrestrained sexual desire and conquest, or to more adventurous societies that admit polygamy. Rauch is actually in the position of a civilizer. And on this I agree with him totally. That is precisely what makes him more open to arguments of marriage traditionalists for strengthening norms of monogamy.

But it sets him against those who, like Dan Savage, argue that legal same-sex marriage will improve all marriages generally by breaking the institution away from patriarchal norms of wifely fidelity and tight gender roles.

Rauch wants marriage to civilize the sexual instinct, even among gay men. Savage and others want the sexual instinct to revise the terms of civilization. If consent is the only standard of legitimacy for a sexual relationship — which is the lesson many have taken from the last 50 years of cultural development — then asking about the social outcomes in polygamous arrangements will be seen as irrelevant or potentially bigoted. This is what happened to all the social science saying that kids do best in stable two-parent biological families when it came to the debates about same-sex family formation.

I agree with Rauch on the goods of a bourgeois society. The question is whether these count in light of the ruling handed down by Justice Anthony Kennedy, and the emerging understanding that sexual relationships cannot be condemned for lack of any quality save consent. Same-sex marriage advanced in our culture in part by the prim aspirations to bourgeois life among gays and lesbians. But it also advanced by stigmatizing religious censures against sexual relationships, the same religious censures that banned polygamy. It advanced by deconstructing the arguments for harnessing the sexual instinct toward civilizing projects, and by proposing in their place a sexual ethic admitting of nothing other than consent, whether that applies to one, two, three, or more partners.

Now Rauch wants to bring back the religious chauvinism of Christian monogamy and a civilizational project to encourage poorer women towards the most marginal male partners? Good luck. That ship has sailed. And his movement christened it.