JONATHAN TURLEY, a law professor at George Washington University, is representing the family featured on the reality show "Sister Wives" in their legal challenge to Utah's law against polygamy. It's a big, unusual family. Kody Brown is "married" to four women and father to 16 children. "One of the marriages is legal", Mr Turley writes, "and the others are what the family calls 'spiritual.' They are not asking for the state to recognise their marriages. They are simply asking for the state to leave them alone." Mr Turley goes on to make what I find to be a persuasive case.

The Browns have been subject to a criminal investigation for more than a year, but are not accused of child abuse or any crime other than having a particular kind of unusual family. Mr Turley notes that other families with similarly unusual structures are not picked out for persecution by the law. "It is widely accepted that a person can have multiple partners and have children with such partners", Mr Turley observes. "But the minute that person expresses a spiritual commitment and 'cohabits' with those partners, it is considered a crime." This certainly seems arbitrary. Indeed, the law positively encourages de facto polygamous families to organise into multiple households lacking the cohesion and economies of our culture's idealised single-household family.

Imagine the family of a twice-divorced, thrice-married woman with one child from each union. Let's say she's a stay-at-home mom who has custody of all the kids, and gets child-support payments from her first two husbands. So, children with three different fathers live together in a single household, supported by a portion of three different mens' income. How is this not de facto polyandry? How significant is it, really, that her first two husbands don't happen to live with their kids and her third husband? Suppose they move in. What then? Is it okay as long as they pay rent? As long as they no longer love the mother of their children, or vice versa? I say it's okay as long as everyone involved says it's okay.

Mr Turley wonders why civil libertarians haven't been more vocal in support of the right of polygamists to be left alone:

The reason might be strategic: some view the effort to decriminalize polygamy as a threat to the recognition of same-sex marriages or gay rights generally. After all, many who opposed the decriminalization of homosexual relations used polygamy as the culmination of a parade of horribles. In his dissent in Lawrence, Justice Antonin Scalia said the case would mean the legalization of “bigamy, same-sex marriage, adult incest, prostitution, masturbation, adultery, fornication, bestiality and obscenity.”

But isn't polygamy, as it actually exists, a backward practice hostile to the interests of women? What about fundamentalist Mormon compounds in which children are raised in isolation, indoctrinated/brainwashed, teenage girls are married off to their uncles and impregnated, while surplus boys are ejected without the tools to cope with the outside world. Mr Turley replies:

Of course, the government should prosecute abuse wherever it is found. But there is nothing uniquely abusive about consenting polygamous relationships. It is no more fair to prosecute the Browns because of abuse in other polygamous families than it would be to hold a conventional family liable for the hundreds of thousands of domestic violence cases each year in monogamous families.

I think this is the right way to think about it. I would add that conventional monogamous marriage was in fact an abusive, exploitative, patriarchal arrangement until very recently. In 1993,North Carolina was the last state to recognise spousal rape as a crime.