Yesterday’s post focused on what marriage is. Today’s explores why the government recognizes marriage in the first place. As my co-authors and I argue in our new book, What Is Marriage? Man and Woman: A Defense, virtually every political community has regulated male-female sexual relationships. Why? Not because government cares about romance as such. It cares about male-female sexual relationships because these alone produce new human beings.

While yesterday’s post focused on the definition of marriage, today’s focuses on the public purpose that marriage plays in a political community. 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.

As the late sociologist James Q. Wilson wrote, “Marriage is a socially arranged solution for the problem of getting people to stay together and care for children that the mere desire for children, and the sex that makes children possible, does not solve.”

Social science confirms the importance of marriage for kids. According to the best available sociological evidence, children fare best on virtually every examined indicator when reared by their wedded, biological parents. Studies that control for other factors, including poverty and even genetics, suggest that children reared in intact homes do best on educational achievement, emotional health, familial and sexual development, and delinquency and incarceration.

Consider the conclusions of the Left-leaning research institution Child Trends:

[R]esearch clearly demonstrates that family structure matters for children, and the family structure that helps children the most is a family headed by two biological parents in a low-conflict marriage. Children in single-parent families, children born to unmarried mothers, and children in stepfamilies or cohabiting relationships face higher risks of poor outcomes. . . . There is thus value for children in promoting strong, stable marriages between biological parents. . . . [I]t is not simply the presence of two parents, . . . but the presence of two biological parents that seems to support children’s development.

Men and women typically bring different strengths to this process, and they are better suited to it the more closely related they are to the children. Fathers are particularly important for child development. Rutgers University sociologist David Popenoe explains:

The burden of social science evidence supports the idea that gender-differentiated parenting is important for human development and that the contribution of fathers to childrearing is unique and irreplaceable.

Popenoe concludes:

We should disavow the notion that “mommies can make good daddies,” just as we should disavow the popular notion . . . that “daddies can make good mommies.” . . . The two sexes are different to the core, and each is necessary—culturally and biologically—for the optimal development of a human being.

Marriage benefits everyone, because separating child-bearing and -rearing from marriage burdens innocent bystanders: not just children, but the whole community. It’s the community that often must step in to provide (more or less directly) for their wellbeing and upbringing. A child born and raised outside marriage is six times more likely to experience poverty than a child in an intact family—and therefore welfare expenditures grow. So by encouraging the norms of marriage—monogamy, sexual exclusivity and permanence—the state is strengthening civil society and reducing its own role.

In other words, the most basic function of limited government—protecting civic order—also justifies legally regulating marriage. So the goals of marriage law—which do not involve banning other consensual relationships—are legitimate for government, even from a libertarian perspective.

Getting government out of the civil marriage business would be a catastrophe for limited government. Abolishing civil marriage would weaken social support for its norms. Over time, the law shapes what people think marriage is—which in turn affects how current and future spouses act.  As countless studies show, absentee fathers and out-of-wedlock births bring a train of social pathologies, and greater demand for policing and social services. This was, after all, what inspired the original “marriage movement,” as my first post explained.

A study by the Left-leaning Brookings Institution finds that $229 billion in welfare spending between 1970 and 1996 can be attributed to the breakdown of the marriage culture and the resulting exacerbation of social ills: teen pregnancy, poverty, crime, drug abuse and health problems. A 2008 study found that divorce and unwed childbearing cost taxpayers $112 billion each year. And Utah State University scholar David Schramm has estimated that divorce alone costs local, state and federal government $33 billion each year.

Civil marriage serves the ends of limited government more effectively, less intrusively, and at less cost than picking up the pieces from a shattered marriage culture.

Of course, it isn’t just the legal title of marriage that encourages adherence to marital norms. There is nothing magical about the word “marriage.” Instead, marriage laws work by embodying and promoting a true vision of what marriage is that makes sense of those norms as a coherent whole.

But marital norms make no sense—as matters of principle—if marriage is just intense emotional regard. There is no reason of principle why emotional union should be permanent. Or limited to two persons, rather than larger ensembles. Or sexual, much less sexually exclusive. Or inherently oriented to family life and shaped by its demands. This isn’t to say that couples couldn’t decide to live out these norms where temperament or taste so motivated them; but that there is no reason of principle to demand it of them. So legally enshrining this alternate view of marriage would undermine the norms whose link to the common good justifies state action in the first place.

And now we can see the link between the central questions in this debate: what marriage is and why the state promotes it. It’s not that the state shouldn’t achieve its basic purpose while obscuring what marriage is. Rather, it can’t. Only when policy gets the nature of marriage right do we reap the civil society benefits of recognizing it.