Yesterday’s post explained government’s policy interest in marriage. Government needs to get marriage policy right, because it shapes the norms associated with this most fundamental relationship.

Redefining marriage would abandon the norm of male-female sexual complementarity as an essential characteristic of marriage. Making that optional would also make other essential characteristics—like monogamy, exclusivity and permanency—optional, as my co-authors and I argue in our new book, What Is Marriage? Man and Woman: A Defense. We also show how it is increasingly confirmed by the rhetoric and arguments of those who would redefine marriage (“revisionists”) and by the policies that their more candid leaders increasingly embrace. Indeed, several commentators on Tuesday’s post explicitly jettisoned monogamy, sexual exclusivity and pledged permanence as demands of marriage.

Consider the norm of monogamy. In testifying before Congress against the Defense of Marriage Act (DOMA), prominent New York University professor Judith Stacey expressed hope that the revisionist view’s triumph would give marriage “varied, creative and adaptive contours . . . [leading some to] question the dyadic limitations of Western marriage and seek . . . small group marriages.”

In their statement “Beyond Same-Sex Marriage,” more than 300  self-styled LGBT and allied scholars and advocates—including prominent Ivy League professors—call for legally recognizing sexual relationships involving more than two partners. University of Calgary professor Elizabeth Brake argues in her book Minimizing Marriage that justice requires using legal recognition to “denormalize the ideal of heterosexual monogamy” and correct for “past discrimination against homosexuals, bisexuals, polygamists and care networks.”

And exclusivity? Andrew Sullivan, who has extolled the “spirituality” of “anonymous sex,” writes in his book Virtually Normal that the “openness” of same-sex relationships could enhance the bonds of husbands and wives:

Same-sex unions often incorporate the virtues of friendship more effectively than traditional marriages; and at times, among gay male relationships, the openness of the contract makes it more likely to survive than many heterosexual bonds. . . . [T]here is more likely to be greater understanding of the need for extramarital outlets between two men than between a man and a woman. . . . [S]omething of the gay relationship’s necessary honesty, its flexibility, and its equality could undoubtedly help strengthen and inform many heterosexual bonds.

Similarly, in a New York Times Magazine profile titled “Married, With Infidelities”, Dan Savage encourages spouses to adopt “a more flexible attitude” about allowing each other to seek sex outside their marriage. A piece titled “Monogamish” in The Advocate, a gay-interest newsmagazine, supports this point still more candidly:

Anti-equality right-wingers have long insisted that allowing gays to marry will destroy the sanctity of “traditional marriage,” and, of course, the logical, liberal party-line response has long been “No, it won’t.” But what if—for once—the sanctimonious crazies are right? Could the gay male tradition of open relationships actually alter marriage as we know it? And would that be such a bad thing?

As the article’s blurb reads: “We often protest when homophobes insist that same-sex marriage will change marriage for straight people too. But in some ways, they’re right.”

These are the words of leading supporters of same-sex marriage. If you believe in monogamy and exclusivity—and the benefits these bring to orderly procreation and child wellbeing—but would redefine civil marriage, take note.

Some revisionists have embraced the goal of weakening the institution of marriage in these very terms. Former President George W. Bush “is correct,” says lesbian journalist Victoria Brownworth in “Something Borrowed, Something Blue: Is Marriage Right for Queers?” “when he states that allowing same-sex couples to marry will weaken the institution of marriage. . . . It most certainly will do so, and that will make marriage a far better concept than it previously has been.” Professor Ellen Willis writing in The Nation celebrates the fact that “conferring the legitimacy of marriage on homosexual relations will introduce an implicit revolt against the institution into its very heart.”

Gay radio host Michelangelo Signorile in Out magazine urged those in same-sex relationships to “demand the right to marry not as a way of adhering to society’s moral codes but rather to debunk a myth and radically alter an archaic institution.” They should “fight for same-sex marriage and its benefits and then, once granted, redefine the institution of marriage completely, because the most subversive action lesbians and gay men can undertake . . . is to transform the notion of ‘family’ entirely.”

The world’s limited experience so far suggests that these ideas play out in policy. Since countries have begun recognizing same-sex unions, officials have proposed bills, made administrative decisions or allowed lawsuits challenging nearly every other traditional norm: Mexico City considered expressly temporary marriage licenses. A federal judge in Utah allowed a legal challenge to anti-bigamy laws. A public notary in Brazil recognized a triad as a civil union, saying in almost so many words that the redefinition of marriage required it: “The move reflected the fact that the idea of a ‘family’ had changed. . . . ‘For better or worse, it doesn’t matter, but what we considered a family before isn’t necessarily what we would consider a family today.’ ”

The New York Times recently reported on a study finding that exclusivity was not the norm among gay partners: “‘With straight people, it’s called affairs or cheating,’ said Colleen Hoff, the study’s principal investigator, ‘but with gay people it does not have such negative connotations.’”

In proponents’ own words, redefining marriage would make individuals less likely to abide by marital norms—precisely the concern that led to the marriage movement in the first place.

But as yesterday’s post showed, the state has an interest in marriage and marital norms because these serve the public good: protecting child wellbeing, civil society and limited government.

Government policy addresses male-female sexual relationships in a way it does not address other relationships because these alone produce new human beings. For highly dependent infants, there is no path to physical, moral and cultural maturity—no path to personal responsibility—without a long and delicate process of ongoing care and supervision. Unless children do mature, they never will become healthy, upright, productive members of society. Marriage exists to make men and women responsible to each other and any children they might have.

And marital norms serve these same ends. The norms of monogamy and sexual exclusivity encourage childbearing within a context that makes it most likely children will be raised by their mom and dad. These norms also help ensure shared responsibility and commitment between spouses, sufficient attention from both parents to their children, and avoid the sexual and kinship jealously that might otherwise be present.

The norm of permanency ensures that children will at least be cared for by their mother and father until they reach maturity. It also provides kinship structure for the interaction across the generations, as elderly parents are cared for by their adult children and help care for their grandkids, without the complications of fragmented step-families.

Again, if you believe in monogamy and exclusivity—and the benefits these bring to orderly procreation and child wellbeing—but would redefine civil marriage, take note.