Black Americans tend to be liberal politically. They are the most reliable components of the Democratic Party's base, with the possible exception of gays, whose causes Democrats and liberals are championing. And yet, black Americans are among the demographic groups most opposed to gay marriage.

This frustrates gay activists and their allies. African-Americans have experienced terrible discrimination. Why aren't they more sympathetic with the discrimination that gays experience? There used to be laws against blacks marrying whites. Just as those racist laws needed to be repealed, surely the laws against men marrying men also need to be repealed. Blacks and gays should be natural allies, liberals are saying.

Of course, some black leaders -- like former presidential candidate and ordained minister Al Sharpton -- follow the party line of the liberal establishment. But across the country, black pastors have been staging rallies against gay marriage. African-Americans bitterly resent the attempt by homosexual activists to appropriate the civil-rights movement for their cause. Even the extremely liberal Congressional Black Caucus has denounced comparisons of the gay-marriage movement to the civil-rights struggles of the 1960s.

"Why are blacks, who know so well the reality of discrimination, so uniformly unsympathetic to the case that the gay community is making?" That question is raised by Star Parker, a black evangelical, in a column for Scripps Howard News Service. She says that the main reason is that the civil-rights movement depended on objective moral truth. Homosexual marriage, on the contrary, depends on a rejection of objective moral truth.

"It is not just that they know when their movement is being hijacked," she quotes Wilfred McClay, history professor at the University of Tennessee, as saying. "It is that the religious sensibility that animated the civil-rights movement, and that is still very much alive in the American black community today, is bound up in a biblical worldview that would no more countenance the radical redefinition of marriage than it would the re-imposition of slavery."

"Blacks know instinctively that the debate on gay marriage is the symptom and not the problem," says Ms. Parker. "They know that the root problem is the implicit de-legitimization and marginalization in the United States today of traditional standards of right and wrong." She argues that it was just such a marginalization of right and wrong that allowed slavery. "Without an anchor in ultimate standards, blacks know that the best politics and law, even in as great a country as ours, can lead anywhere."

Concepts such as justice, freedom, and human rights depend on a worldview that recognizes transcendent, objective, moral truths. If morality is just something that we can construct and reconstruct according to our own preferences, as postmodernists believe, then justice, freedom, and human rights will be in jeopardy. To reject universal teachings about sexual morality and to presume to redefine marriage to include homosexual relationships may seem kind and tolerant. But that comes with a horrible price, the repudiation of the very moral framework that makes kindness and tolerance possible.

One might say that black Americans are suffering the consequences of the sexual revolution. The whole culture has drifted away from sexual morality, and African-Americans have been paying the highest price, in the troubled children, the crime, and the poverty that accompany communities that do without marriage. But whites as well as blacks are affected by the moral breakdown. Among white women, Ms. Parker points out, the incidence of out-of-wedlock births is 25 percent -- what it was for black women 40 years ago.

The civil-rights movement of the 1960s was moral. The gay-rights movement is not. It is that simple. Perhaps African-Americans and their churches could start exerting the moral leadership that our whole country desperately needs. —•