The media claim we don’t exist. OK, that’s a slight exaggeration. But after all, we’re Millennials, born during the Reagan administration. We’re supposed to be of the generation that is embracing same-sex marriage in droves.

Instead, we’re standing strong on upholding the truth about what marriage is.

We’ve been asked—repeatedly—whether the position we’re promoting is pointless. Are we willing to endure cultural scorn for holding to a position as supposedly outmoded as natural marriage?

Politicos and pundits offer hyperbolic missives on how conservatives are losing young Americans, who are likely to be more libertarian on social issues. The preferred talking point is to assert the demise of the opposition; Same-sex marriage is “inevitable.”

A justly revered conservative columnist, George F. Will, has said twice on ABC’s “This Week” that opposition to same-sex marriage is a dying trait. “Quite literally,” he said, “the opposition to gay marriage is dying. It’s old people.”

Tweet to Mr. Will: Reports of our death have been greatly exaggerated. #NotDeadYet

Languishing in Obscurity

Every generation will witness to the truth that marriage—the union of a man and woman, husband and wife, father and mother—is the very institution that determines whether our civilization stands or falls. Americans will not stay silent on cherishing and promoting this truth.

The most fundamental unit of society, marriage is founded on the anthropological truth that men and women are different and complementary, the biological fact that the union of a man and woman also creates new life, and the social reality that children need a mom and a dad.

Marriage reflects these realities that are unique to our gendered selves: Man and woman come together as husband and wife to be a father and mother to any children their union produces.

All the polls and court rulings in the world cannot undo the truth that the union of a man and woman is unique among human relationships. But they can obscure these truths, make it less likely that men and women commit to each other permanently and exclusively. This in turn reduces the odds that children will know the love and care of their married mother and father.

No doubt the youngest generation of Americans has shifted on redefining marriage. And there are strong cultural and intellectual currents in opposition to the truth. But this makes sense. America has experienced a slow erosion of marriage over the past 50 years that is now culminating in the view that marriage must be redefined to include same-sex relationships. Americans with same-sex attractions aren’t to blame for this, but redefining marriage will only further weaken our marriage culture.

In the 1960s, heterosexuals, acting on the destructive liberal ideology of the  “Me Generation,” increasingly began to debase human sexuality and the marital relationship. As a result of the sexual revolution and the introduction of no-fault divorce laws, marriage became an institution more about the desires of adults than the needs of children—an institution that need not even aspire to permanency. In the eyes of marriage revisionists, marriage was about adult emotional union and sex became more casual—something conquerable, rather than embraced for what it could beget: children.

Laws and cultural practices shape belief; belief shapes behavior. So it is little surprise that when the law redefined marriage through no-fault divorce that Americans changed their behaviors, with divorce rates rising from single digits to nearly 50 percent. This culture focused on adult romance—that a marriage should last only so long as the love does—is what today’s Millennials have inherited.

Long Erosion

Same-sex marriage is, in a certain sense, a logical progression in the erosion of the meaning of marriage. The question facing Americans now is whether we will further abandon the norms of marriage—monogamy, sexual exclusivity and permanency—and promote the collapse of the institution by fundamentally redefining it.

Consider some of the costs. The American experiment of tampering with marriage has been one of heartache and despair. The historical record is not fun to tell. Many were led to believe that more liberalized understandings of marriage and sexuality would mean the liberation of individuals from an archaic, oppressive institution.

The opposite has proven true. Today, 40 percent of all children are born outside marriage (over 70 percent among black Americans). The easy attitude about divorce is fully ingrained in the public conscience. Broken homes only perpetuate further brokenness, ensnaring all in an endless cycle of poverty and government dependency. The welfare state increasingly steps in to fill the role of absent parent; government means-tested assistance providing cash, food, housing, medical care and social services to poor and low-income single parents amounted to $330 billion in 2011.

The situation is familiar, as even President Barack Obama has said: “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.”

Fathers matter, and marriage helps to connect fathers to mothers and children.

Defending marriage is not about reclaiming a vestigial social unit of yesteryear. Marriage is a universal human good that puts the interest of civilization as a first priority.

For decades, social science has shown that children tend to do best when reared by their married mother and father. Government recognizes marriage because it is an institution that benefits the public good. It is an institution unlike any other.

Marriage is society’s least restrictive means to ensure the well-being of future citizens. State recognition of marriage protects children by incentivizing adults to commit permanently and exclusively to each other and their children.

The movement to redefine marriage in America grew in the space of a few years without rigorously examining the potential impact of changing society’s most fundamental institution. Americans have not counted the cost of redefining marriage.

Obvious Effects

Redefining marriage would further distance it from the needs of children and deny, as a matter of policy, the ideal that children need a mother and a father.

Redefining marriage would diminish the social pressures and incentives for husbands to remain with their wives and their biological children, and for men and women to marry before having children. The concern is not so much that a relatively small number of gay or lesbian couples would be raising children; rather, it would be difficult for the law to send a message that fathers matter when the law has redefined marriage to make fathers optional.

In recent decades, as already noted,  marriage has been weakened by a revisionist view that marriage is more about adults’ desires than children’s needs. This view reduces marriage primarily to emotional bonds or legal privileges. Redefining marriage represents the culmination of this revisionism and would leave emotional intensity as the only thing that sets marriage apart from other bonds.

However, if marriage had to do only with intense emotional regard, marital norms would make no sense. No reason of principle requires an emotional union to be permanent. Or limited to two persons. Or sexual, much less sexually exclusive (as opposed to “open”). Or inherently oriented to family life and shaped by its demands.

In other words, if sexual complementarity is optional for marriage, then almost every other norm that sets marriage apart is optional, too.

Redefining marriage, of course, further marginalizes those with traditional views and erodes religious liberty. The law and culture would seek to eradicate such views through economic, social and legal pressure. Believing what virtually every human society believed until the past decade or so—that marriage is the union of a man and woman ordered to procreation and family life—increasingly would be seen as a malicious prejudice to be driven to the margins of culture.

The consequences for Christians and other religious believers already are apparent. After Massachusetts redefined marriage to include same-sex relationships, Catholic Charities of Boston was forced to discontinue adoption services rather than place children with same-sex couples against its principles. Massachusetts public schools began teaching elementary-age children about same-sex marriage, defending their decision as showing they are “committed to teaching about the world they live in, and in Massachusetts same-sex marriage is legal.” An appeals court ruled that parents have no right to opt out of these classes.

The Becket Fund for Religious Liberty reports that “over 350 separate state anti-discrimination provisions would likely be triggered by recognition of same-sex marriage.”

The Marriage Movement

Long before Americans debated same-sex marriage, another debate launched what came to be called the “marriage movement.” Its purpose was to explain why marriage was good for the men and women who were faithful to its demands, and for the children they reared.

Articles in mainstream magazines—including Barbara Dafoe Whitehead’s 1993 cover story for The Atlantic, “Dan Quayle was Right”—documented how family fragmentation was wreaking havoc on society. In 1996, Mike and Harriet McManus launched Marriage Savers to combat marital breakdown. In 2001, Wade Horn championed the Healthy Marriage Initiative for the Bush administration.

Such efforts—from Focus on the Family’s ministries to various fatherhood initiatives—targeted high divorce rates and the rising birth rate for unmarried women. Same-sex marriage wasn’t on anyone’s radar. The concern of the marriage movement leaders, like that of today’s leading conservative scholars and activists, was much broader.

So it’s not surprising that one of the most prominent opponents of redefining marriage, Maggie Gallagher, was active in the marriage movement throughout the 1980s and ’90s. She wrote a book in the late ’80s on how the sexual revolution was “killing family, marriage and sex” and “what we [could] do about it.” Then, her 2000 book made “the case for marriage,” showing the many ways that marriage is better for couples than cohabitation.

The question of whether to redefine marriage to include same-sex relationships didn’t take center stage until 2003, when the Massachusetts Supreme Court claimed to find a constitutional right to that recognition. Those who had led the marriage movement for decades had to ask themselves: Would recognizing same-sex relationships as marriages strengthen the marriage culture, or weaken it?

Lessons from the Past

That’s the backdrop of the debate that Americans (especially Millennials) are having. Some wonder why conservatives choose to focus exclusively on same-sex marriage. The answer is simple: We don’t.

First, conservatives always did—and still do—make other social and political efforts to strengthen the marriage culture. The push for same-sex marriage was brought to us. Second, now that this is the live debate, we can’t ignore it. The outcome will have wider effects on the marriage culture.

Taking a long view of history, we believe America and Western civilization will self-correct on marriage over time—regardless of polls or Supreme Court rulings. A historical parallel helps explain our optimism. The experiences of the early pro-life movement—a beleaguered, criticized few—shed revealing light on how to navigate political and cultural forces that want to shut down debate.

It’s instructive to consider the Supreme Court’s 1973 decision in Roe v. Wade. After that ruling, many of America’s cultural elites considered the abortion debate settled. But 40 years later, the debate continues and the pro-life movement has made considerable gains in reviving a culture of life.

But that didn’t look likely in the years just after Roe, when public opinion shifted strongly in favor of abortion access. With each passing day, it seemed, another pro-life figure—Ted Kennedy, Jesse Jackson, Al Gore, Bill Clinton—would switch to embracing abortion on demand, attempting to predict how the political calculus would affect election outcomes and electoral appeal.

The elites ridiculed pro-lifers as being anti-woman, as “on the wrong side of history.” The pro-life ranks were aging; their children, increasingly against them. Even the Southern Baptists were supportive of Roe. It looked like a losing battle. How easy it would have been just to give up and go home.

But courageous Americans refused to sit silently by. And now the pro-life side has turned the tide in key areas of the struggle. On the question of the humanity of the child in the womb, pro-lifers have won the intellectual battle decisively. Today, most Americans oppose most abortions. On the state level, pro-life laws proliferate.

Looking to the Future

There are lessons here. Today’s young people have the blessing of inheriting pro-life arguments, organizations, and strategies. Now we have to do that work on a new issue. Arguments can change minds.

Christians who have embraced a faulty view of marriage can be converted. Whatever journalists, intellectuals and other elites may tell us, the only way to guarantee a political loss is to sit idly by. We must frame our message, strengthen coalitions, devise strategies and bear witness.

Witness to the truth matters for its own sake. However, persistent, winsome witness also tends to produce good fruit, even if it takes 40 years and counting. In this struggle to preserve marriage, we need to take that long view—one that doesn’t look to immediate wins or losses, but decade-long paradigm shifts that reshape how Americans think about marriage.

So, we’re optimistic for two reasons. First, as young people settle down, marry and have kids, they’ll develop greater appreciation for what makes a marriage and for the gendered nature of parenting. They’ll come to see that husbands and wives aren’t interchangeable, and that mothers and fathers aren’t either.

Second, if we are correct about the likely harms of redefining marriage, then even a season of experiencing genderless marriage and its consequences in some places will lead to a reassessment. After all, the harms of divorce and non-marital childbearing led to the marriage movement of the 1980s and ’90s.

It’s not accurate to say the times have relegated the defense of marriage to the geriatric ward. And there’s no such thing as being on the “right” or “wrong” side of history. There’s only being on the right or wrong side of truth.

What’s next on the marriage front? Americans committed to marriage coming out of the shadows. Moving forward to rebuild marriage begins with refusing to remain silent.

Why? Because we cannot stay silent about the truth of what marriage is, and the manifold ways it builds the America we all long for.

-Ryan T. Anderson, 31, is the William E. Simon Fellow in Religion & a Free Society at The Heritage Foundation and co-author of the book What is Marriage? Man and Woman: A Defense. Andrew T. Walker, 27,  is a policy analyst in Heritage’s DeVos Center for Religion and Civil Society.