One of the clearest things about Minnesota's new gay-marriage law is that it requires Minnesotans to "play pretend" — to embrace obvious fictions as reality.

For example, the law states that citizens must view the union of two people of the same sex — who can't produce a child — as identical to that of a man and woman, whose sexual complementarity is the only thing that can. The law also declares that, henceforth, "when necessary to implement the rights and responsibilities of spouses or parents in a civil marriage between persons of the same sex," words like "mother" and "father" "must be construed in a neutral manner to refer to a person of either gender" under Minnesota law. But a woman can't be a father, and a man can't be a mother. It's a biological fact Minnesota lawmakers can't repeal, no matter how much they wish to.

Our lawmakers seem utterly untroubled by their vote to impose a regime of "let's pretend." What explains this?

The legislators and their supporters who celebrated the bill's passage on the State Capitol lawn made clear that what they crave is to be in the vanguard of a brave new world. "By your political courage you join that pantheon of exceptional leaders who did something extraordinary," Gov. Mark Dayton proclaimed as he signed the law. "You changed the course of history for our state and our nation." President Obama received similar accolades when he announced his support for gay marriage. Apparently, for some folks, there's nothing headier than to be on the Right Side of History.

But here's a dirty little secret. No one has the remotest idea where our state officials' decision to turn our fundamental social institution upside down will take our society in coming decades. We know the experiment is starting out badly, because it's based on pretending that demonstrable falsehoods are true. We have no idea what ripple effects it will have, how its redefinition of parenthood will affect children, or whether we'll next see a push for marriage as the union of three or more loving people: the logical next step.

You would expect our legislators to wrestle with weighty questions like these before deciding to end marriage as we — and all other people on Earth — have always known it. They did not. That's because they (at least the true believers among them) were motivated by a quasi-religious faith that "marriage equality" will inevitably lead our state to the secular equivalent of the Promised Land.

Gay marriage is a crusade, and the driving force behind it is the secular religion of progressivism. This faith's adherents put their hope, not in salvation after death, but in a hazy and glorious future here on Earth.

The journalist Christopher Caldwell has put it succinctly: "The argument for gay marriage is always made in the name of history — not the history we have lived, but the history we are yet to live." Will that future turn out as planned? Progressive dogma leaves no doubt that it must. Those who dare to question this — like gubernatorial candidate Tom Emmer or Chick-fil-A president Dan Cathy — are branded heretics, and figuratively burned at the stake by the media, Hollywood and fervent wavers of the Rainbow Flag.

Social commentator George Weigel sees the roots of the progressive faith in an "intense revival" of an ancient religious movement called Gnosticism. This movement has taken many forms throughout history. But it is always an elite phenomenon, and always holds that the key to human flourishing is possession of a special knowledge that allows man to transcend the material world, so he can build paradise for himself on his own terms.

Modern man — at least many intellectuals — chafes under the constraints of reality. He longs to be "as a god," to pretend that there are no givens, that "everything in the human condition is plastic and malleable." In short, says Weigel, he craves to believe that "everything can … be bent to human willfulness, which is to say, human desire."

Today, Gnosticism is most "powerfully embodied" in the Sexual Revolution and its ideology of gender, writes Weigel. That ideology holds that maleness and femaleness — two elements of the human condition that have always been understood as the essence of "givenness" — are now to be viewed as mere cultural constructs.

Weigel points to Spain's Zapatero government, which passed a law in 2007 permitting men to change themselves into women, and vice versa, by a declaration at a government office — absent any surgery — after which a new national identity card, with the new gender, is issued. "It is hard to imagine a more explicit expression of personal willfulness overpowering natural givenness," he concludes.

The gay marriage crusade is just the latest manifestation of the secular religion of America's intellectual elites. Who knows what new game of "let's pretend" our chattering classes will impose on us next?

Katherine Kersten is a senior fellow at the Center of the American Experiment. The views expressed here are her own. She is at kakersten@gmail.com.