It would be disastrous for the justices to do so. They would repeat the error in Roe v. Wade: namely, trying to remove a morally charged policy issue from the forums of democratic deliberation and resolve it according to their personal lights.

Even many supporters of legal abortion now consider Roe a mistake. Lacking any basis in the text, logic or original understanding of the Constitution, the decision became a symbol of the judicial usurpation of authority vested in the people and their representatives. It sent the message that judges need not be impartial umpires-as both John Roberts and Sonia Sotomayor say they should be-but that judges can impose their policy preferences under the pretext of enforcing constitutional guarantees.

By short-circuiting the democratic process, Roe inflamed the culture war that has divided our nation and polarized our politics. Abortion, which the Court purported to settle in 1973, remains the most unsettled issue in American politics-and the most unsettling. Another Roe would deepen the culture war and prolong it indefinitely.

Some insist that the Supreme Court must invalidate traditional marriage laws because "rights" are at stake. But as in Roe, they are forced to peddle a strained and contentious reading of the Constitution-one whose dubiousness would undermine any ruling's legitimacy.

Lawyers challenging traditional marriage laws liken their cause to Loving v. Virginia (which invalidated laws against interracial marriages), insinuating that conjugal-marriage supporters are bigots. This is ludicrous and offensive, and no one should hesitate to say so.

The definition of marriage was not at stake in Loving. Everyone agreed that interracial marriages were marriages. Racists just wanted to ban them as part of the evil regime of white supremacy that the equal protection clause was designed to destroy.

Opponents of racist laws in Loving did not question the idea, deeply embodied in our law and its shaping philosophical tradition, of marriage as a union that takes its distinctive character from being founded, unlike other friendships, on bodily unity of the kind that sometimes generates new life. This unity is why marriage, in our legal tradition, is consummated only by acts that are generative in kind. Such acts unite husband and wife at the most fundamental level and thus legally consummate marriage whether or not they are generative in effect, and even when conception is not sought.

Of course, marital intercourse often does produce babies, and marriage is the form of relationship that is uniquely apt for childrearing (which is why, unlike baptisms and bar mitzvahs, it is a matter of vital public concern). But as a comprehensive sharing of life-an emotional and biological union-marriage has value in itself and not merely as a means to procreation. This explains why our law has historically permitted annulment of marriage for non-consummation, but not for infertility; and why acts of sodomy, even between legally wed spouses, have never been recognized as consummating marriages.

Only this understanding makes sense of all the norms-annulability for non-consummation, the pledge of permanence, monogamy, sexual exclusivity-that shape marriage as we know it and that our law reflects. And only this view can explain why the state should regulate marriage (as opposed to ordinary friendships) at all-to make it more likely that, wherever possible, children are reared in the context of the bond between the parents whose sexual union gave them life.

If marriage is redefined, its connection to organic bodily union-and thus to procreation-will be undermined. It will increasingly be understood as an emotional union for the sake of adult satisfaction that is served by mutually agreeable sexual play. But there is no reason that primarily emotional unions like friendships should be permanent, exclusive, limited to two, or legally regulated at all. Thus, there will remain no principled basis for upholding marital norms like monogamy.

A veneer of sentiment may prevent these norms from collapsing-but only temporarily. The marriage culture, already wounded by widespread divorce, nonmarital cohabitation and out-of-wedlock childbearing will fare no better than it has in those European societies that were in the vanguard of sexual "enlightenment." And the primary victims of a weakened marriage culture are always children and those in the poorest, most vulnerable sectors of society.

Candid and clear-thinking advocates of redefining marriage recognize that doing so entails abandoning norms such as monogamy. In a 2006 statement entitled "Beyond Same-Sex Marriage," over 300 lesbian, gay, and allied activists, educators, lawyers, and community organizers-including Gloria Steinem, Barbara Ehrenreich, and prominent Yale, Columbia and Georgetown professors-call for legally recognizing multiple sex partner ("polyamorous") relationships. Their logic is unassailable once the historic definition of marriage is overthrown.

Is this a red herring? This week's Newsweek reports more than 500,000 polyamorous households in the U.S.

So, before judging whether traditional marriage laws should be junked, we must decide what marriage is. It is this crucial and logically prior question that some want to shuffle off stage.

Because marriage has already been deeply wounded, some say that redefining it will do no additional harm. I disagree. We should strengthen, not redefine, marriage. But whatever one's view, surely it is the people, not the courts, who should debate and decide. For reasons of both principle and prudence, the issue should be settled by democratic means, not by what Justice Byron White, in his dissent in Roe, called an "act of raw judicial power."

----Mr. George is professor of Jurisprudence at Princeton University and founder of the American Principles Project (www.americanpriniplesproject.org)