This new morality is a form of libertarianism (people have a right to do as they please) whose fundamental principle is a simplistic idea of fairness (if you can do it, so can I). I learned about libertarian fairness many years ago as a father of small children, whose ultimate argument upon being denied something they wanted invariably was, "It isn't fair."

Childish it may be, but it resonates with baby-boomers and members of Generation X, to say nothing of today's kids. Nearly all of them have been steeped in the conviction that fairness is the all-but-exclusive norm of morality, and fairness means giving everybody what he or she wants -- especially if it's something that somebody else already has.

A federal district judge in San Francisco has recently ruled that California's Proposition 8, defining legal marriage in that state as a relationship between a man and a woman, violates the constitutional guarantees of due process and equal protection. Proposition 8, adopted by California voters two years ago after the state supreme court had legalized same-sex marriage, clashes with "the state's interest in equality," said Judge Vaughn Walker. In other words, it isn't fair.

The case now goes to the liberal 9th U.S. Circuit Court of Appeals. Regardless of what happens there, the ruling almost certainly will be appealed to the U.S. Supreme Court. With its present membership, the Supreme Court probably divides 4-4-1 on same-sex marriage -- four justices in favor of legalization, four justices opposed, and, as so often, Anthony Kennedy the swing vote.

It's not unreasonable to suppose that President Barack Obama's two Supreme Court picks, Sonia Sotomayor and Elena Kagan, are among the four justices in favor. People who oppose same-sex marriage would be well advised to pray for long life and good health for Roberts, Scalia, Thomas, and Alito.

On the other hand, proponents of same-sex marriage are said to fear that too sweeping a victory too soon -- such as a decision on the order of Judge Walker's hubristic reading of the Constitution -- could produce results like those of Roe v. Wade, the 1973 decision in which the Supreme Court abruptly imposed legalized abortion on the entire country.

As matters now stand, 30 states limit legal marriage to man-woman unions; five states and the District of Columbia recognize same-sex unions as marriages. Across-the-board legalization of gay marriage by the Supreme Court in one swoop might generate a lasting backlash and energize the culture war.

One often hears it said that public opinion is shifting in favor of same-sex marriage, and there's evidence that it is. Although 52 percent of California voters two years ago backed Proposition 8, a recent poll found that 51 percent of Californians support gay marriage now.

But this is hardly surprising, in view of the intense propagandizing for same-sex marriage in media and the academic world, and the squishiness in liberal religious sectors. Indeed, all things considered, it's remarkable that that opposition remains as strong as it does in the face of constant repetition of the libertarian "fairness" argument combined with the firestorm of verbal abuse directed at those who disagree.

Since the rules of engagement in a pluralistic secular democracy don't permit one to say simply that gay sex is a sin which the law shouldn't encourage, the best argument against legalizing same-sex marriage is the harm done to traditional marriage.

No-fault divorce provides a precedent here. Changing the meaning of marriage to accommodate libertarian morality -- which essentially is what happened in this case -- contributed to the weakening of traditional marriage visible in statistics of recent decades.

Declaring "the trend lines are not healthy," Allan Carlson, a scholar and advocate of traditional marriage, points out that between 1980 and 2007 the marriage rate (per 1,000 unmarried women) fell from 61.4 to 39.2 -- a decline of 36 percent -- while the absolute number of marriages fell from 2.39 million in 1980 to 2.16 million in 2008. Allowing same-sex couples to marry might nudge these figures up a bit, but no one imagines it will have that result for traditional marriage.

Approval of no-fault divorce didn't produce these declines all by itself, any more than legalization of same-sex marriage would do. But in combination with other cultural factors, such experiments in redefining marriage plainly contribute to that result.

In his splendid new study of the thinking of John Paul II, Theology of the Body in Context (Pauline Books & Media), theologian William E. May writes that civil society "must respect the dignity of marriage and the family and refuse to dignify as 'marriage' and accord the same rights to nonmarital unions." And because no society can afford to be permissive about something as fundamental as marriage and family, he insists, the Church is obliged to speak up in their defense.

Indeed yes. But in speaking up, expect to hear someone on the other side growl, "It isn't fair." Think of those guys playing chess on the tennis court.

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