AFTER GAY MARRIAGE, what will become of marriage itself? Will same-sex matrimony extend marriage's stabilizing effects to homosexuals? Will gay marriage undermine family life? A lot is riding on the answers to these questions. But the media's reflexive labeling of doubts about gay marriage as homophobia has made it almost impossible to debate the social effects of this reform. Now with the Supreme Court's ringing affirmation of sexual liberty in Lawrence v. Texas, that debate is unavoidable.

Among the likeliest effects of gay marriage is to take us down a slippery slope to legalized polygamy and 'polyamory' (group marriage). Marriage will be transformed into a variety of relationship contracts, linking two, three, or more individuals (however weakly and temporarily) in every conceivable combination of male and female. A scare scenario? Hardly. The bottom of this slope is visible from where we stand.

Advocacy of legalized polygamy is growing. A network of grass-roots organizations seeking legal recognition for group marriage already exists. The cause of legalized group marriage is championed by a powerful faction of family law specialists. Influential legal bodies in both the United States and Canada have presented radical programs of marital reform. Some of these quasi-governmental proposals go so far as to suggest the abolition of marriage.

The ideas behind this movement have already achieved surprising influence with a prominent American politician. None of this is well known. Both the media and public spokesmen for the gay marriage movement treat the issue as an unproblematic advance for civil rights. True, a small number of relatively conservative gay spokesmen do consider the social effects of gay matrimony, insisting that they will be beneficent, that homosexual unions will become more stable.

Yet another faction of gay rights advocates actually favors gay marriage as a step toward the abolition of marriage itself. This group agrees that there is a slippery slope, and wants to hasten the slide down. To consider what comes after gay marriage is not to say that gay marriage itself poses no danger to the institution of marriage. Quite apart from the likelihood that it will usher in legalized polygamy and polyamory, gay marriage will almost certainly weaken the belief that monogamy lies at the heart of marriage. But to see why this is so, we will first need to reconnoiter the slippery slope. Promoting polygamy DURING THE 1996 congressional debate on the Defense of Marriage Act, which affirmed the ability of the states and the federal government to withhold recognition from same-sex marriages, gay marriage advocates were put on the defensive by the polygamy question.

If gays had a right to marry, why not polygamists? Andrew Sullivan, one of gay marriage's most intelligent defenders, labeled the question fear-mongering -- akin to the discredited belief that interracial marriage would lead to birth defects. 'To the best of my knowledge,' said Sullivan, 'there is no polygamists' rights organization poised to exploit same-sex marriage and return the republic to polygamous abandon.' Actually, there are now many such organizations. And their strategy -- even their existence -- owes much to the movement for gay marriage.