Last Friday, a U.S. District Court struck down a central part of the Utah statute that outlaws polygamy. The ruling was not just a victory for the husband and wives who had brought the suit to court—Kody, Meri, Janelle, Christine, and Robyn Brown, who belong to a Mormon splinter church called the Apostolic United Brethren and star in a reality TV show called Sister Wives. Nor was it merely a victory for families with more than two spouses. It was a victory for sane public policy.

The case is drenched in the politics of polygamy, but in one important way it isn't about polygamy at all. The Browns all live together, but only one of the wives has a marriage license. To the extent that their family departs from American marital norms, it is a private arrangement unrecognized by the state. The Browns' household is more like the informal and contractual gay unions that have existed for decades than the fully recognized same-sex marriages that many states are beginning to allow today.

And that's all that is now legal. Previously, Utah considered a person guilty of bigamy if, "knowing he [or she] has a husband or wife or knowing the other person has a husband or wife, the person purports to marry another person or cohabits with another person." It is the final part of that restriction—the bit about cohabitation—that comes into play here. If a dozen roommates in San Francisco decide to set up a polymorphous polyamorous partnership, the law would have nothing to say about the matter. (The building code enforcers might object, I suppose. But that's a separate issue.) Utah's rules are different, and they are different because of a long legacy of prejudice and religiously targeted persecution. Pointing to this persecution and to a history of selective enforcement, Judge Clark Waddoups ruled that the portion of the statute prohibiting cohabitation violates the First Amendment's guarantee of religious liberty. Pointing to other matters of law, such as the fact that Utah no longer has common-law marriages, he ruled that the ban on "purport[ing] to marry another person" should apply only to someone attempting or pretending to acquire more than one marriage license. That puts households like the Browns' in the clear.

So Utah is not about to start recognizing group marriages. It's just going to stop bringing criminal charges against people who have done nothing more than establish their own unlicensed big-love homes. Whether or not you agree with Waddoups' legal reasoning, as a matter of policy the new order is vastly preferable to the old. Indeed, this case demonstrates just how misguided a crackdown on polygamy can be.

The most common argument against tolerating plural marriages is that they are often associated with abuse. There are stories of desert sects forcing women into marriage, of girls raped by their elders, of boys being abandoned instead of letting them grow up to compete for scarce wives. Terrible, unconscionable stuff. Yet the Sister Wives case makes it clear that, no matter how exploitative some plural marriages may be, that does not mean they all are. The court's decision notes that "There has been no allegation of child or spousal abuse by members of the Brown family" and that "No member of the Brown family has ever been charged with a crime." To punish the Browns because of crimes committed by other polygamists would be discriminatory and perverse. Indeed, it would divert resources that could be spent ferreting out the genuine abusers.

This ferreting, in turn, was harder to do because plural marriage was a felony. That broad bigamy statute drove entire subcultures underground. It gave non-abusive polygamists an incentive not to come forward when they learned about abuses in other homes. It exacerbated the problems that the law was supposed to solve. By tolerating plural marriage, Utah will allow more sunshine to fall on it.

Nor does this decision stumble into the thorny issues raised by the idea of licensing these marriages. There are non-trivial questions of how the tax, welfare, and immigration systems would handle a world where the state recognizes, as opposed to merely tolerates, polygamous and polyamorous unions. I don't think those issues are insurmountable, and I think a strong case for fully legal plural marriages can be made; but in this case, you don't need to make it. The state of Utah isn't being ordered to revamp its family law. It is being ordered to revamp its criminal code. It will now be both easier to combat genuine crimes and easier for nonviolent nonconformists to live their lives without fear of arrest. That's two reasons to cheer the decision.