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Will the gay marriage debate ever end? I’m not just talking about the political or legal fight. I’m talking about the culture war. Supporters of same-sex marriage liken it to interracial marriage, an idea that once seemed bizarre to most Americans but is now almost universally accepted. Opponents of gay marriage liken it to abortion, which continues to divide and inflame the country. Which way will this battle go?

Until now, I thought it would rage on. Same-sex marriage is far more radical than interracial marriage. It challenges our basic understanding of the institution. You can’t expect people to accept such a change overnight.

But now I see a way out. Tuesday’s Supreme Court hearing on Proposition 8, which banned same-sex marriage in California, has exposed the exit route. People who oppose gay marriage can come to accept it as moral, once they understand homosexuality as a kind of infertility.

The telltale exchange took place about half an hour into the hearing. Justices Stephen Breyer and Elena Kagan challenged a central premise of Proposition 8: that gay couples should be excluded from marriage because the purpose of marriage is procreation. Breyer and Kagan asked Charles Cooper, the lawyer defending Proposition 8, why, in that case, the law allows infertile heterosexual couples to marry. Cooper replied that “society's interest in responsible procreation isn't just with respect to the procreative capacities of the couple itself.” Every marriage, he noted, reinforces “the marital norm, which imposes the obligations of fidelity and monogamy.”

Cooper argued that when one partner is infertile, this norm deters the fertile partner from “irresponsible procreative conduct outside of that marriage.” But he and other defenders of Proposition 8 have invoked this idea more broadly. In a brief filed with the court last fall, Cooper and his clients contended that marriage among infertile heterosexual couples “furthers society’s interest in responsible procreation” in part “by strengthening the social norm that sexual relationships between men and women should occur in marital unions.” Two months ago, 19 states filed an amicus brief reinforcing this point. The procreative “purpose of traditional marriage,” they wrote,” is not “undermined by marriages among the infertile, the elderly, or those who simply choose not to have children. Opposite-sex couples without children who are married model the optimal, socially expected behavior for other opposite-sex couples whose sexual intercourse may well produce children.”

Robert George, the intellectual leader of the resistance to gay marriage, agrees. In a separate amicus brief, he explains that “even an obviously infertile couple” can

“live out the features of true marriage, and so contribute to a strong marriage culture. This makes couples who might conceive more likely to form a marriage and abide by its norms. … 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.”

A brief filed by other conservative scholars extends this line of reasoning. “Marriage is an essential social paradigm, a model, a norm that teaches, guides, and molds,” they observe. In this way,

“Even couples who neither have nor rear children set an important example for those that may. Married infertile couples still support the norm that sexual relationships between men and women should take place within marriage. Their observance of vows of faithfulness reinforces the social norm that children should ideally enjoy the security, nurture, and love of their father and mother and not be subject to the turbulence of impermanent couplings that lead to motherless or fatherless families.”

This is a powerful argument. It focuses not on diversity or equality but on conservative principles of character formation: models, expectations, culture, obligations, responsibility, faithfulness, permanence. Even couples who can’t fulfill marriage as a biological ideal can, and should, reinforce it as a norm.

If you’re liberal, you may hate this argument. But if you’re socially conservative, it’s your gateway to accepting gay marriage. Once you acknowledge that homosexuality is involuntary and immutable, you can start to think about it the way you think about infertility. Your son or daughter, or your neighbor’s son or daughter, may have been dealt a difficult hand. Make the best of it. Encourage these people to embrace marriage as fully as they can.

Depending on how you define it, infertility affects 9 percent of women and perhaps 15 percent of couples. That’s far more common than homosexuality. Beyond age 50, as Kagan points out, the infertility rate among women is 100 percent. Extending marriage rights to all these people hasn’t destroyed the marital norm. It has bolstered it. Gay marriage does the same. It domesticates sex and affirms the simple values of commitment and mutual responsibility. It doesn’t make straight people gay, promiscuous, or indifferent to parenthood. It sets a good example for them.

Don’t take my word for it. Read the briefs against same-sex marriage. They explain all too cogently how infertile couples strengthen the marital norm. All you have to do is recognize what the authors failed to see: Millions of these couples are gay.

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Read more from Slate’s coverage of gay marriage cases at the Supreme Court.