A recent New York Times Magazine article spotlighted a shocking vestige of our nation’s racism: segregated proms. It focused on one school in Georgia’s Montgomery County, though the practice is common across the rural South.

I say “shocking” even though I personally wasn’t surprised. One of my best friends is from rural Tennessee. His alma mater still segregates superlatives: White Most Likely to Succeed, Black Most Likely to Succeed; Funniest White, Funniest Black, and so on.

The white students quoted in the Times article expressed some reservations about the practice, but generally concluded with “It’s how it’s always been…It’s just a tradition.” In the words of Harley Boone, a platinum blond girl with beauty-queen looks who co-chaired last year’s white prom, “It doesn’t seem like a big deal around here. It’s just what we know and what our parents have done for so many years.”

“It’s just what we know.” Miss Boone reminded me of another beauty queen, in both her appearance and her comment: Miss California USA Carrie Prejean.

Miss Prejean, you’ll recall, when asked her beliefs about marriage equality, responded (in part), “I believe that a marriage should be between a man and a woman. No offense to anybody out there, but that’s how I was raised.”

How I was raised. Tradition. What our parents have done. This is not, in itself, a bad reason for doing something. It explains why I set the table the way I do, for instance, or why I always put an extra unlit candle on a birthday cake (”good luck for the next year,” my mom always told me). It explains, too, more substantial practices—how we gather, celebrate milestones, express joy, or mourn loss. No generation does, or should, invent everything from scratch.

And yet, sometimes “what we know”—or thought we knew—stops working, or never worked very well in the first place.

I used to load the dishwasher with the forks tines down—because that’s how my parents did and still do it—until I realized they get cleaner tines up (in my dishwasher, anyway, and please don’t send me irate e-mails if yours is different).

Spotty forks are one thing. Racial and sexual inequality are quite another. When traditions cause palpable harm to people, it’s time to change. At that point, rethinking tradition is not merely optional, as in the dishwasher case—it’s morally mandatory.

And that’s why Prejean’s ” how I was raised” comment struck so many of us as a dumb answer. No educated person can justifiably claim ignorance of the challenges gay individuals and couples face. We gays are deprived of a fundamental social institution, treated unequally in the eyes of the law, and told that our deep, committed, loving relationships are inferior, counterfeit, or depraved. In the face of such injustice, “that’s how I was raised” sounds hollow and cowardly.

There are those who bristle at any analogy between homophobia and racial injustice. Indeed, a favorite new right-wing strategy is to claim that liberals unfairly label as “bigots” anyone who opposes same-sex marriage, even on the basis of sincere moral and religious convictions.

But that’s one reason why the analogy is so powerful, and so revealing. It shows that citing “sincere moral and religious convictions” doesn’t get one a free pass for maintaining unjust institutions.

No analogy compares two things that are exactly the same. (That would not be an analogy, but an identity.) Analogies compare two or more things that are similar in some relevant respect(s). The similarities can be instructive.

The white citizens of Montgomery County, Georgia, seem like a nice enough bunch. They don’t carry pitchforks or wear hooded robes. I doubt that Miss Boone ever uses the n-word, although her grandparents probably do. (Mine did, too, until we grandchildren protested loudly enough.) They are otherwise decent folk misled by powerful tradition.

I’m sure that, pressed for further explanation, many of these folks could make the right noises about doing what’s best for their children and eventual grandchildren. And much like “that’s just what we know,” that response would sound familiar. Opponents of marriage equality use it constantly.

But don’t marriage-equality opponents have social-science data backing them up? They don’t. Yes, they have data about how children fare in fatherless households, for example, and then they extrapolate from that data to draw conclusions about lesbian households. The problem is that there are too many confounding variables. So then they fall back on their “vast untested social experiment” argument: we just don’t know how this is going to turn out. Which, again, is precisely the sort of thing we might expect the Montgomery parents to say to justify their “tradition.”

From the fact that two groups of people use the same forms of argument, it doesn’t follow that their conclusions are equally good or bad. It depends on the truth of their premises.

Still, the tendency of both segregationists and marriage-equality opponents to hide behind “that’s how I was raised” provides a powerful analogy—in moral laziness.

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John Corvino, Ph.D. is an author, speaker, and philosophy professor at Wayne State University in Detroit. His column “The Gay Moralist” appears weekly on 365gay.com. Read more about him at www.johncorvino.com.

John will be a volunteer faculty member this summer for Campus Pride’s Leadership Camp for GLBT students. For more about Campus Pride’s work, or to make a donation on John’s behalf to support this year’s program, visit http://www.campuspride.org/.