With divorce rates high, out-of-wedlock births rampant, and most kids fated to spend at least some of their childhood in single-parent homes, the American family obviously has some serious problems. Tom Green is not one of them.

Whatever else you can say about Green, you can't say he's done anything to weaken the American family. On the contrary, he takes the concept of "family man" to heroic lengths. The 52-year-old Utahan is "married" to five wives, and they have borne him 29 children. Green is a polygamist—one of thousands of so-called Mormon fundamentalists who insist on living in accordance with the church's original practice. And that is what led to his recent conviction on four counts of bigamy, which could send him to prison for 25 years.

Conservatives, who have not been heard defending Green, might find a lot to like in him. He's a devout Christian who asks only to be left alone to practice his faith. His household conforms to a model that has prevailed in much of the world for much of human history. Polygamy has ample sanction in the Bible, having been practiced by King David and King Solomon, the latter of whom had 700 wives. It also has deep roots in the ultra-wholesome Church of Jesus Christ of Latter-day Saints: Early Mormon leader Brigham Young fathered scores of children by his more than 20 wives. The church abandoned plural marriage in 1890 in the face of the federal government's fierce efforts to stamp it out. Today, however, the church prescribes excommunication for anyone practicing polygamy. But not all Mormons think the government needs to take action. Utah Gov. Mike Leavitt—who says his "great-great-great grandfather had many families"—has given a state appointment to a leader from a polygamist community, not to mention suggesting that plural marriage might be a constitutionally protected exercise of religious freedom.

Most Americans are marital Unitarians—believing in, at most, one spouse. To any male acquainted with marriage, a houseful of wives sounds less like a nonstop orgy than an endless siege of PMS. The attractions are even slimmer for women—most of whom, given the option of having 20 percent of a particular husband, would doubtless think that was 20 percent too much. Sharing a man and a home with several other women sounds about as alluring as repeal of the 19th Amendment. As for offspring, most parents lose enough sleep over how to put two or three children through college. Twenty-nine would induce howling terror.

But the fact that it will always be a minority taste doesn't explain why plural marriage should be illegal. Given the current state of sexual and social mores in America, after all, what used to be the scandalous element of polygamy—one man enjoying the sexual favors of multiple women—barely qualifies as PG-13. Serial polygamy, which is what you might call marrying and then divorcing one person after another, has also become commonplace. No law prevents a man from having five sexual partners or 500. Hugh Hefner, fueled by Viagra, has multiple girlfriends sharing his bed in the Playboy mansion, but no prosecutor has seen fit to indict him. Countless professional athletes leave trails of illegitimate children from coast to coast without suffering so much as a minor scandal.

The law, in short, doesn't prevent a man from being licentious, promiscuous, irresponsible, and thoroughly goatish. Had Green just shacked up with a harem of willing single women, no one would have cared. But when he lives as a dutiful husband to five women in a collection of trailer homes in the Utah desert, he somehow presents a dire threat to our social foundation. This brings to mind heterosexuals accusing homosexuals of undermining marriage, even as heterosexuals have left it in tatters. The argument for allowing polygamy has much in common with the argument for letting gays enter into matrimony. If consenting adults who prefer polygamy can do everything else a husband and wife can do—have sex, live together, buy property, and bring up children jointly—why should they be prohibited from legally committing themselves to the solemn duties that attach to marriage? How is society worse off if these informal relationships are formalized and pushed toward permanence?

Critics have a ready answer: because polygamy, as currently (and surreptitiously) practiced in Utah and neighboring states has been rife with abuses—including forced marriages, sexual exploitation of minors, and welfare dependency. Green is a prime example: He married one of his wives when she was 13, and he was convicted not only of bigamy but of criminal nonsupport for failing to repay the state more than $50,000 in welfare benefits for his children. Other male polygamists have been convicted of child abuse and incest. A Salt Lake Tribune investigation found that a polygamous community on the Utah-Arizona border has one of the highest rates of welfare participation in the West.

But such unsavory conduct stems partly from the fact that when polygamy is illegal, the only people likely to practice it are nut cases and people with a deep-seated contempt for authority. Plural marriage, in this group, may be just one of many expressions of aggressive noncomformity. If the practice were legally permitted, on the other hand, it would be more likely to attract people with a strong law-abiding disposition. The need to stay under the radar of law enforcement agencies also breeds abuse by discouraging its victims from going to the authorities. Legalizing the practice would bring polygamists out from underground, making it easier to combat the real evils found in some plural marriages. Those who persist in such abuses can be prosecuted along with all the other pedophiles and welfare frauds—the vast majority of whom, it will surprise you to learn, are non-polygamous.

But what state would play the role of social pioneer? In Utah (along with Arizona and New Mexico), the state constitution has a provision forbidding polygamy that is "irrevocable without the consent of the United States"—which is not likely to be forthcoming. But Douglas Laycock, a religious-freedom authority at the University of Texas law school, says the restriction is clearly unconstitutional—leaving Utah free to repeal the ban anytime it wants.

Anti-polygamy laws can also be challenged as a violation of the privacy rights upheld in a series of Supreme Court cases, including Roe v. Wade. In 1986, the court rejected a claim that these decisions had fatally undermined laws against sodomy. Why? Because, unlike cases involving bans on contraceptive sales and abortion, "no connection between family, marriage, or procreation on the one hand and homosexual activity on the other has been demonstrated." With polygamy, by contrast, the connections are inescapable: "It involves family, it involves marriage, and it involves a whole lot of reproduction," says Laycock.

Nor is that the only basis for a constitutional challenge. In 1996, the Supreme Court court struck down a Colorado constitutional amendment prohibiting local governments from passing laws banning discrimination based on sexual orientation. The justices said the measure was illegal because it targeted one group, gays, for unfavorable treatment. No less an authority than Justice Antonin Scalia, writing in dissent, said the reasoning casts serious doubt on state constitutional bans on plural marriage. Polygamists, he wrote, "have been 'singled out' by these provisions for much more severe treatment than merely denial of favored status; and that treatment can only be changed by amendment of the state constitutions. The court's disposition today suggests that these provisions are unconstitutional, and that polygamy must be permitted in these states."

Scalia's prediction notwithstanding, the courts aren't likely to lead the way to tolerance of polygamy. So that's up to Utah, Arizona, or another of those states where polygamists have persisted in following their beliefs despite legal and social ostracism. The history of American society in recent years has been the rapid expansion of diversity—and the broad acceptance of different cultures, beliefs, and customs. Why should an ancient form of marriage remain beyond the pale? In our time, the American family has been transformed in all sorts of ways, many of them malign. Next to those changes, Tom Green is no threat.