Listen to William Saletan’s closing remarks at the Fixed Point Foundation’s same-sex marriage debate. 

Several weeks ago, I debated gay marriage in Alabama, where same-sex marriage is still broadly opposed. The debate was hosted by a conservative Christian organization, the Fixed Point Foundation, and many people in the audience shared its views. I argued not for “marriage equality” but for a less radical idea: that same-sex couples are much like infertile heterosexual couples, whose non-procreative unions are already accepted within the framework of traditional marriage. I’ve condensed the argument here in the hope that Slate readers might share it with friends, relatives, or colleagues who, for religious or other reasons, remain uncomfortable with homosexuality. I also hope you’ll share the audio of the closing speech from the debate, which the foundation has kindly allowed Slate to publish above. The foundation has made video of the debate available here.

If you’ve always understood marriage to be the union of a man and a woman, the idea of letting a gay couple marry may seem strange. Maybe you were taught that homosexuality is wrong. Or maybe you worry that if we change the male-female rule of marriage, other rules, such as monogamy and lifetime commitment, will also change.

Fortunately, there’s a way to accept gay marriage without overturning traditional marriage.

The first thing to understand is that homosexuality isn’t a sin. It can’t be, because it isn’t a choice. It’s not like promiscuity or premarital sex or cheating on your spouse. It’s just the way some people are born. If you’re not sure about this, talk to people who are gay. They’ll tell you that they didn’t choose to be gay, just as you didn’t choose to be straight. Their lives would be a lot easier if they could switch. Many of them have tried. They’ve learned the hard way that they can’t change their sexual orientation any more than you can change yours.

The second thing to recognize is that homosexuality isn’t harmful. It’s not like pedophilia or sexual abuse. And it’s not a lifestyle, though people often use that term. A gay person can be just as conventional (and even boring!) as a straight person. If your son fell in love with a woman, you’d want him to be a faithful and devoted husband to her. What if your daughter, too, fell in love with a woman? Would that make her less moral? It might be hard to understand. But couldn’t she be a faithful and devoted spouse, just like your son?

One thing that distinguishes homosexuality from sexual perversion is that the attraction itself is natural. Nearly all of us, gay or straight, were born with one of the world’s two most common sexual orientations: an orientation toward women or an orientation toward men. In a small percentage of cases, people who are oriented toward women are born female, and people who are oriented toward men are born male. That doesn’t mean these people can’t live happy, healthy lives. But it does impair their ability to have a family. If your child is born gay, he’ll never be able to have a baby with the person he loves.

That’s sad. But once you realize that he can’t change either part of the equation—his body or his orientation—you can understand his situation the same way you’d understand it if he fell in love with a woman and couldn’t have a baby with her. Infertility, like homosexuality, isn’t the norm. But it does happen in nature, and we don’t condemn the affected couples for violating the natural order. We just ask them to make the best of their situation.

That’s the simplest way to make sense of homosexuality. Treat it as a kind of infertility. When we talk about infertility in couples, we usually don’t assume that both partners are sterile. We just mean that they can’t make a baby together. That’s the way it is for gay couples. We don’t ask infertile straight couples to divorce or break up so they can go have a baby with someone else. We shouldn’t do that to gay couples, either. And we don’t tell an infertile woman that she has to stay unmarried and celibate her whole life. We know that wouldn’t be fair. It would be just as unfair to do that to a woman who was born gay.

Many people worry that if we let same-sex couples marry, we’ll confuse the meaning of marriage and lose our reverence for the traditional union of man and woman. But same-sex marriage is already legal in dozens of states, and there’s no evidence that it has weakened heterosexual marriage. In fact, homosexuality isn’t the first exception we’ve made to the traditional model of marriage. We’ve been making exceptions all along.

The simplest example is old people. Sherif Girgis, the scholar who debated this issue with me at a recent forum sponsored by the Fixed Point Foundation, says the defining purpose of traditional marriage is procreation. But we routinely allow marriages between people who are too old to procreate. According to the Census Bureau, 400,000 women ages 45 or older get married in this country in a single year. More than 160,000 of these women are 55 or older. More than 45,000 are 65 or older.

Even if you could get pregnant at 45, or by some miracle at 55, you’re not getting pregnant at 65. So when you apply for a marriage license and write down your age, we know you’re not going to have a baby, just as surely as if you were marrying a person of the same sex. But we let you get married anyway. Why?

Girgis has a good answer. He and his co-authors, Robert George and Ryan Anderson, have written a book on this subject. It’s titled What Is Marriage? They explain how all marriages serve the moral health of the community: “Even an obviously infertile couple can live out the features of true marriage, and so contribute to a strong marriage culture.” The example set by these couples “makes couples who might conceive more likely to form a marriage and abide by its norms,” the authors observe. “The more spouses (including infertile ones) reflect by their lives the truth about what marriage requires, the more saturated we will all be in those truths, so that more families with children will stay intact.”

That’s an excellent point: Even a childless couple can model the virtues of marriage. But why isn’t that just as true of gay couples? They can’t make straight people gay, any more than heterosexual marriages can make gay people straight. A married couple, gay or straight, can influence by its example only the voluntary aspects of marriage: commitment and monogamy.

In this way, same-sex marriage can promote traditional values. When the gay couple next door gets hitched, how do you—a straight guy shacking up with your girlfriend—explain why you haven’t popped the question?

The bottom line, either way, is that we don’t have to abandon the traditional definition of marriage. That definition has always made an exception for infertile couples, based on the moral example these couples reinforce. Gay couples fit this exception. Like other infertile couples, they don’t reflect the biological norm. But they do reflect—and promote—the moral norm. And that’s what matters.