Same-sex marriage never will be widely accepted in America for a simple reason: It’s based on a lie. But don’t take my word on this; leading LGBT scholars and activists say as much.

Take Masha Gessen, acclaimed author and former Russian director of Radio Liberty. “Fighting for gay marriage generally involves lying about what we are going to do with marriage when we get there — because we lie that the institution of marriage is not going to change,” Gessen said last year. 

Last month, I was part of a debate at NYU Law School at which Judith Stacey, a sociology professor at the university, declared: “Children certainly do not need both a mother and a father.”

Stacey went on to suggest that three parents might be better than two. In fact, while asserting she is in favor of same-sex marriage because of “equal justice,” Stacey admitted she isn’t a fan of marriage. “Why should there be marriage at all?” she asked.

I pointed out that marriage exists, and the government takes an interest in marriage, because the sexual union of a man and a woman produces children — and children need a mom and a dad.

I quoted President Obama making a closely related point:

“We know the statistics — that children who grow up without a father are five times more likely to live in poverty and commit crime; nine times more likely to drop out of schools and 20 times more likely to end up in prison. They are more likely to have behavioral problems, or run away from home, or become teenage parents themselves. And the foundations of our community are weaker because of it.”

Stacey’s response? President Obama “was deeply misled.” Indeed, “Obama was dead wrong.”

But most Americans know that on this point, Obama is right. Children are better off with a mom and a dad. And marriage is the institution that unites a man and a woman as husband and wife to be father and mother to the children their union produces.

Obama is wrong, though, in his “evolved” thinking that we can redefine marriage to make fathers optional while still insisting that they are essential. This inherent contradiction empowers those who want to weaken the foundation of the nuclear family.

Take Stacey, for example. In congressional testimony against the Defense of Marriage Act, she expressed hope that redefining marriage would give marriage “varied, creative and adaptive contours,” including “small group marriages.”

Stacey was among more than 300 scholars and advocates who signed a statement, “Beyond Marriage,” calling for legal recognition of sexual relationships involving more than two partners. During our NYU debate, she asserted that nothing gives the state an interest in monogamy.

The very day of the debate, Slate posted an article headlined “Legalize Polygamy!” The author, Jillian Keenan, argues: “Just like heterosexual marriage is no better or worse than homosexual marriage, marriage between two consenting adults is not inherently more or less ‘correct’ than marriage among three (or four, or six) consenting adults.”

She concludes: “Legalized polygamy in the United States is the constitutional, feminist and sex-positive choice.”

And this is why the marriage redefiners are doomed to fail: Redefinition has no logical stopping point. Its logic leads to the effective elimination of marriage as a legal institution. This will harm women, children and society as a whole.

If we redefine marriage to exclude the norm of men and women complementing each other in (ideally) a lifelong familial bond, Gessen admits, “The institution of marriage is going to change, and it should change … I don’t think it should exist.”

What an amazing claim: Radical advocates of same-sex marriage don’t think marriage should exist, at least not as a state-sponsored institution. They think marriage is simply an intense emotional union — whatever sort of interpersonal relationship consenting adults want it to be.

Their victory would leave marriage with no essential features, no fixed core as a social reality. And if marriage has no form and serves no essential purpose, how would society protect the needs of children — the prime victims of our non-marital sexual culture — without government growing more intrusive and more expensive?

Same-sex marriage rejects the anthropological truth that men and women are different and complementary, the biological fact that reproduction depends on a man and a woman and the social reality that children need both a mother and a father.

In the end, the truth about marriage will win out.

-Ryan T. Anderson is the William E. Simon Fellow in Religion and a Free Society at The Heritage Foundation. He is co-author of the book “What Is Marriage? Man and Woman: A Defense.”