At the heart of modern America’s heavy reliance on constitutional law to settle issues that more properly would be decided in the political process is something called “the rationality test.” The legions of lawyers and judges who purport to understand and enforce our Constitution actually know little about that document. What they usually apply when addressing society’s divisive issues is a free-floating demand that government policies be rationally related to some legitimate purpose.

This demand sounds innocuous enough. Who, after all, is in favor of irrational laws? But in actual operation, it is the judiciary’s use of the rationality test that is intellectually empty. Indeed, as demonstrated by Judge Vaughn Walker’s August 4 opinion invalidating California’s ban on homosexual marriage, judicial application of the rationality test can be a parody of intelligent analysis.

Step back and consider the scene. Judge Walker held a trial to determine whether millions of people living in widely varying circumstances across many centuries had any legitimate reason at all for defining marriage as a union between a man and a woman. To make this assessment, the judge needed from those challenging the law only eight lay witnesses and nine expert witnesses. He needed 16 days of trial time. And, of course, he had to apply his own formidable mind to the problem. After bringing the judgment of history before this tribunal, Judge Walker concluded that there was no evidence justifying the traditional definition of marriage. Indeed, the issue did not even present “a debatable question.”

Now, the good judge took pains to present himself as a workmanlike lawyer rather than a recklessly arrogant philosopher king. His opinion is designed so that it appears merely to apply legal propositions laid down by the Supreme Court and to evaluate factual evidence meticulously. Courts routinely do these tasks, so this decision, we are to believe, is all in a day’s work.

If Walker’s application of the rationality test was so straightforward, you might well ask, how could he conclude with such certitude that all those people​—the many millions who have thought traditional marriage to be a bedrock of society—have been entirely wrong? And you might also wonder how he could assert, despite the fierce debate Americans have been having about gay marriage, that there is actually nothing to discuss.

Here is how it works: Where there are undeniably reasons (debatable reasons, to be sure) behind the traditional definition of marriage, Judge Walker simply announces that those reasons are illegitimate and therefore don’t count. And where the reasons are undeniably legitimate, Judge Walker dismisses them on the basis of sweeping factual claims that he cannot possibly support.

Consider the argument that homosexual conduct is immoral or, at least, less desirable than heterosexual conduct. Needless to say, many highly thoughtful people throughout history have held such views and have given reasons to support them. To the extent that these reasons are religious, Judge Walker rejects them on the ground that it is impermissible to base public policy on religious ideas.

This radical idea has some vague resonance with certain understandings of the Establishment Clause, but it is in fact not the law. It is simply a baseless edict that, if taken seriously, would silence some of the most important arguments that have been made in favor of policies on, for example, civil rights and the death penalty. Not to mention freeing the slaves.

Of course, not all moral arguments against homosexuality are religiously based. Judge Walker discards all the secular moral arguments on the basis of a puzzling assertion, repeatedly made in the opinion, that moral disapproval is “not enough” to justify a public policy. The closest the judge comes to giving a reason for this dismissal of the importance of moral judgment is his occasional use of the adjective “private” to modify “moral views,” as if there were certain moral positions on the institution of marriage that are inherently private and therefore can’t be used to satisfy the demand for rational justification.

The simple fact is that, despite the patina of legal authority alluded to in Walker’s opinion, religious and moral reasons are not illegitimate bases for public policy. And the traditional definition of marriage is rationally related to those reasons.

When Judge Walker cannot dispense with a justification because it is supposedly illegitimate, he dismisses it on the basis of factual assertions that are highly controversial at best. Take the argument that the California law was justified as an attempt to proceed with caution on a risky change in social norms. Walker responds that “proponents presented no reliable evidence that allowing same-sex couples to marry will have any negative effects on society.” See, no need to be cautious because the judge already knows what all the effects of homosexual marriage will be.

California voters, it goes without saying, did not conclude that homosexual marriage would involve risk on the basis of the meager evidence produced in Judge Walker’s courtroom. They proceeded on the basis of historical understandings and their own experience—neither of which was Judge Walker in any position to evaluate.

In at least one place, however, Judge Walker’s opinion actually seems to insist that there can be no risk in allowing same-sex marriage because that innovation would not change the historical understanding of marriage. He says same-sex marriage would be “an evolution in the understanding of gender rather than a change in marriage.” The exclusion of homosexuals from marriage is, the judge explains, “an artifact of a time when the genders were seen as having distinct roles in society and in marriage.” That time, he opines confidently, “has passed.” Left unexplained is how a trial judge can know that the genders are no longer seen as having distinct roles in society and marriage. Isn’t disagreement about that issue one cause of the current battle over gay marriage?

Despite all its cerebral and legalistic trappings, Judge Walker’s opinion is not an exercise in some detached and impartial form of rationality. Like the law it invalidated, his opinion is a reflection of aspirations, fears, guesses, and moral judgments. In political debate, people generally make no pretense about the controversial and uncertain nature of their arguments. Most jurists, in contrast, believe that judicial application of the “rationality test” is different from political argumentation. It is thought to be a high intellectual exercise that constrains the worst excesses of political decision making. What is at least as frightening as the unruly world of politics is the supercilious and resolutely self-satisfied world occupied by judges like Vaughn Walker.

Robert F. Nagel is the Rothgerber professor of constitutional law at the University of Colorado Law School.

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