By Ben Boychuk and Joel Mathis

A federal judge last week struck down part of Utah's ban on polygamy - the state can no longer prosecute adult men and women who "cohabitate" in numbers larger than the traditional pair. Critics suggested the ruling was a natural next step after the success of same-sex marriage campaigns and lawsuits in recent years.

But Kody Brown, the fundamentalist Mormon "Sister Wives" star whose case sparked the ruling, proclaimed it a victory for religious freedom.

Is polygamy inevitable? Are we headed down the slippery slope? Joel Mathis and Ben Boychuk, the RedBlueAmerica columnists, debate the issue.

JOEL MATHIS

What's sacred to one person is often profane to another. Obvious, yes, but a point often in need of deep reconsideration.

Need proof? Here's my sparring partner, Ben Boychuk, commenting two weeks ago on whether Hobby Lobby should be forced to abide by Obamacare mandates to provide birth-control coverage to its employees: "The First Amendment is supposed to be a bulwark against government encroachment on the free exercise of religion."

He's (ahem) making a somewhat different argument this week.

Yes, it is a bit hilarious to watch the same conservatives - who were just passionately advocating the inviolable importance of the First Amendment - suddenly remember other priorities. It helps you understand that when they say "religious liberty," they often mean "Christian privilege," and no, the two are not the same.

Now, I don't want to be in the position of defending polygamy. While there may be exceptions, it appears to me that women in such situations are usually less than full partners - often bound to such relationships before (and whether or not) they give their full consent. That's bad.

Understand, though, the state of Utah wasn't just denying Kody Brown legal recognition for his multiple relationships - it was denying that Brown and his "sister wives" even have the right to live in the same place. That's a rather considerable intrusion on personal freedom, if you think about it. The state needs a rational basis, a showing of legitimate harm, to interfere with such freedoms - and no, general squeamishness doesn't suffice.

Critics say the Utah decision was made possible by the logic of the 2002 Supreme Court decision striking down laws banning homosexual conduct. They are right about that and there's no point in denying it; they are wrong in suggesting it means the end of the world. It might get messy at times, but we'll get it worked out. In the meantime: Civilization will chug along, much as it always does.

BEN BOYCHUK

Liberals favor a broad reading of the Bill of Rights - until they don't. Does it matter that polygamy was illegal everywhere in America when the states ratified the First Amendment in 1789? Not at all, our liberal friends say.

Our "living" Constitution all but requires Americans to accept that standards evolve and truths are negotiable. Times change.

So liberals agree religious liberty should be absolute - unless your beliefs collide with the prevailing progressive orthodoxy. In that case, kindly shut up and knuckle under. It's the American way.

That's a far cry from the Founders' view, which flatly rejected that just any claim to religious liberty was legitimate. The Aztecs, for example, believed human sacrifice was a religious duty. No one would accept murder as "free exercise of religion" - well, almost no one. We're a big country. Somebody, somewhere might think human sacrifice is copasetic, just as a lot of people have convinced themselves polygamy is just fine.

Times really do change. Republicans in their 1856 platform urged Congress "to prohibit . those twin relics of barbarism, polygamy and slavery."

Every school child today understands slavery was wrong. It deprived humans of their natural liberty. What about polygamy?

Polygamy says one woman isn't enough for a man. (Polyandry, which involves one wife and multiple husbands, is rare.) That's also what our sexually liberated society says. Has the serial "hookup" culture liberated women? Would legalized polygamy be any better?

As the U.S. Supreme Court underscored in a famous 1878 ruling, "(P)olygamy leads to the patriarchal principle, and which, when applied to large communities, fetters the people in stationary despotism, while that principle cannot long exist in connection with monogamy."

In other words, polygamy was - and remains - wrong because it undermines the essential equality between one husband and one wife.

It somehow seems fitting that the federal judge in Utah ruled on a case brought by the patriarch of a reality TV show. Those nice people on TV seem to make it work, right? And if the effect is to further undermine an institution essential for maintaining a free society - well, that would make for a fine show, too.

Ben Boychuk is associate editor of the Manhattan Institute's City Journal. Joel Mathis is a contributing editor to Philadelphia Magazine.