There's a lot to love about this week's federal court ruling striking down Oklahoma's gay marriage ban. Among other things, it dismantles the crucial but thin argument that banning gays from getting wed does anything to protect marriage: “Excluding same-sex couples from marriage has done little to keep Oklahoma families together thus far, as Oklahoma consistently has one of the highest divorce rates in the country.” It also rigorously reviews the relevant history of the state's anti-gay law and notes that its champions defended the law by calling it an effort to “uphol[d] morality” and ensure that only “what God has ordained as traditional marriage” would be recognized by state law—both constitutionally impermissible rationales for a law.

But the otherwise admirable decision by Judge Terence Kern raises an important concern about how we as a nation have come to define—and apply—“morality.” Kern cites the Supreme Court's now firmly established precedent that moral belief, on its own, cannot serve as the basis for passing a discriminatory law. As Sandra Day O'Connor wrote in her 2003 concurring opinion in the court's decision striking down sodomy bans, “We have never held that moral disapproval, without any other asserted state interest, is a sufficient rationale … to justify a law that discriminates among groups of persons.” Kern concludes that, following from the court's precedent, states must now “demonstrate that their laws rationally further goals other than promotion of one moral view of marriage.”

But what does Kern mean by “one moral view of marriage.” To understand what he's getting at, it's important to first summarize the most compelling (but not ultimately persuasive) argument against same-sex marriage. When not relying on morality, religion, or simple tradition, most people who oppose gay marriage cite kids—creating them and nurturing them. Some worry that having gay parents is bad for kids and that blessing gay unions by legalizing them makes gay parenting more likely. Others worry that letting gays wed could make straights less likely to marry, resulting in more out-of-wedlock births and the social harms associated with them. In either case, the argument boils down to one of norms: Broadening the definition of marriage to include gays, these folks believe, could change people's understanding of the institution and affect their behavior in ways that have adverse consequences to society. Gay marriage, as the conservative Witherspoon Institute puts it in a passage quoted by the Oklahoma court, could “further undercut the idea that procreation is intrinsically connected to marriage … further weakening the societal norm that men should take responsibility for the children they beget.”

Would that really happen? Would straight people decline to marry just because gay people can? They haven't so far, as Slate reported in analyzing data in states with gay marriage. But the test of a law's constitutionality doesn't always have to rely on empirical reality. To determine if a law has a rational relationship to an important government interest—and is therefore constitutional—a court must, as Judge Kern explains, “not only consider the actual purpose of the law but also whether there are any other justifications that could ‘conceivably' provide a rational reason for its passage.”

The question thus becomes: Why would straight people change their marriage behavior in response to gay marriage? If it's because they simply don't like gay people and wouldn't want to join a club that admits them as members, such moral disapproval is an impermissible basis for a law. Kern astutely notes the possibility that many champions of protecting the “traditional family”—who swear they have nothing against gays but insist they must be shut out of marriage to ensure that straights still sign up—are claiming to promote the family as “a guise for singling out same-sex couples for different treatment due to ‘moral disapproval.' ”

Judge Kern concludes from all this that the “negative impact” argument—that expanding the parameters of marriage could irreparably harm the whole institution—is “impermissibly tied to moral disapproval of same-sex couples.” It's here that I think Kern goes too far and gets it wrong. The perceived threats posed by gay marriage, he writes “are to one view of the marriage institution—a view that is bound up in procreation, one morally ‘ideal' parenting model, and sexual fidelity” (which Witherspoon and others have wrongly suggestedgay couples tend to “downplay”). Kerns' point seems to be that the very notion that marriage could or should play a role in encouraging people to commit to relationships for the good of their kids is an impermissible basis to make marriage law, because it's rooted in a moral judgment about what's good and bad. That's just silly. When society collectively deems peace or prosperity to be worthy goals that laws can properly seek to encourage, it is expressing “one moral view” of those goals—that they're good things we should aim to achieve to maximize human welfare. Society has to be able to base laws on that kind of moral judgment, or it won't be able to work toward a collective good. Confusion about this is one more reason that the right's obsession with so-called moral issues like homosexuality has been so harmful, and the left's reaction—to flee use of the whole concept of morality—is another.

What courts really mean—or should mean—in barring “moral disapproval” as the basis for laws is that arbitrary moral disapproval is improper, not all moral disapproval. The taboo against homosexuality is an arbitrary moral disapproval. Homosexuality harms no one. It's not, it turns out, a morally bad thing at all. It's just that lots of people and lots of big religions have subscribed to this taboo for so long that it became acceptable to simply deem gayness immoral. What people really mean when they call homosexuality immoral, for the most part, is either that they find it icky or that their religion forbids it—and for no discernable reason, or at least not one that has any capacity to help make life better or worse for people in today's world, the true basis of morality. Indeed, despite huge recent advancements in tolerance of gay people, homosexuality stands virtually alone as the one thing Americans are comfortable calling “immoral” without ever having to explain why. (Last year, a Georgetown University poll found that even the famously tolerant youth cohort is “nearly evenly divided over whether sex between two adults of the same gender is morally acceptable.”)

Judge Kern finds that “preclusion of ‘moral disapproval' as a permissible basis for laws aimed at homosexual conduct or homosexuals represents a victory for same-sex marriage advocates.” That's surely true, but it's too bad that it is. Same-sex marriage, or any other dimension of gay equality, should not be reachable only by banning consideration of right and wrong altogether. In our fight to throw off an ancient and senseless deployment of moral judgment, we shouldn't lose sight of the uses of morality altogether. A truly good society still relies on it.