Single mothers (and occasionally fathers) find it much more difficult to be the kind of autonomous, self-supporting individuals that our system of government was designed for. Single parents turn to the government for assistance in dozens of ways. Pearlstein cites economist Benjamin Scafidi, who has offered a rough calculation of how much family breakdown costs American taxpayers annually. Scafidi considered TANF (Temporary Assistance to Needy Families), Food Stamps, housing assistance, Medicaid, S-Chip, child welfare services, justice system costs, WIC, LIHEAP (Low Income Home Energy Assistance Program), Head Start, school breakfast and lunch programs, and foregone tax receipts. The annual bill to taxpayers: $112 billion.

But Scafidi was being conservative, Pearlstein argues. He didn't include the Earned Income Tax Credit, the costs to schools that accrue from additional discipline problems, the special education costs that increase in lock step with chaotic family environments, and the added burdens on Medicare and Medicaid that result from more unmarried older Americans. Scafidi explains that "high rates of divorce and failure to marry mean that many more Americans enter late middle age (and beyond) without a spouse to help them manage chronic illnesses, or to help care for them if they become disabled."

The flight from marriage is transforming the complexion of American society -- increasing inequality and decreasing self-sufficiency. As Kay Hymowitz has written (soon to be joined by new books by Charles Murray and the above mentioned Pearlstein), marriage patterns are creating a caste system in a country that had traditionally enjoyed relative equality. Among the well-educated, marriage rates have remained very stable over the past several decades. College graduates are thus (mostly) rearing their children in orderly, supportive environments in which kids are taught to study hard, delay gratification and plan for the future. But 54 percent of the children of high school dropouts are illegitimate. Their parents' lives are marked by financial stress, conflict and turmoil.

Since income and education are so closely linked, the outlines of a permanent caste system become visible, with the educated raising children who have the tools to become successful themselves and the poor and lower middle class continuing to give birth under circumstances that virtually condemn their children to poverty.

Much has been made by Democrats of the increasing inequality of income distribution in America. That inequality is real. But it's not the result of tax cuts. It's an artifact of family structure. And unless we find a way to discourage unwed childbearing and revive marriage, the chasm between classes will continue to grow.

Gay marriage is a distraction. The country depends on traditional marriage.