PROFESSOR McLANAHAN’S studies over the years, and many others like them, show that the primary risks associated with single motherhood arise from financial insecurity. They also offer evidence that, to a lesser extent, particular romantic patterns of the mother — namely introducing lots of boyfriends into children’s lives — contribute to the risk. What the studies don’t show is that longing for a married father at the breakfast table injures children.

And Professor McLanahan’s findings suggest that a two-parent, financially stable home with stress and conflict would be more destructive to children than a one-parent, financially stable home without stress and conflict.

There is no doubt, however, that single motherhood can be more difficult than other kinds of motherhood. In France, the response to the added difficulty is to give single mothers preferential access to excellent day care. Here the response is moralism disguised as concern and, at other times, simply moralism.

The idea of “single mothers” may itself be the convenient fiction of a fundamentally conservative society. In fact women move in and out of singleness, married parents break apart, men and women live together without marrying, spouses or partners die, romantic attachments form and dissolve. Those who brandish research like Professor McLanahan’s ongoing Fragile Families study and Paul R. Amato’s 2005 paper on changing family structures to critique “single mothers” conveniently ignore the fact that such investigations rely on shifting, differing and extremely complex definitions of the households involved.

What gets lost in the moralizing conversation is that there is a huge, immeasurable variety in households, and there are great ones and terrible ones, arduous ones and inventive ones, drab ones and exuberant ones, among families of all structures and economic strata.

It’s useful and humbling to remember that no family structure guarantees happiness or ensures misery: real life is wilier and more fraught with accident and luck than that. If you think that being married ensures a good life for your children you need only enter a bookstore and open any novel, or go to the theater and watch practically any play, or have dinner with nearly anyone you know. Suffering is everywhere, and married parents, even happily married parents, raise screwed-up or alcoholic or lost children, just as single parents raise strong, healthy ones. What matters most, it should go without saying, is the kind of parent you are, not whom you sleep with, and even that matters only up to a point.

With the steep rise of children born to unmarried parents, America’s prevailing fantasies of family life no longer match the facts on the ground. But as the children born to unmarried women under 30 come of age in the majority, these faded archetypes will have to evolve. Our narrow, constricting, airless sense of the isolated nuclear family has not always, if we are honest, served us well, and it may now be replaced by something more vivid and dynamic, and closer to the way we are actually living.

All of the liberal concern about single motherhood might more usefully be channeled into protecting single mothers, rather than the elaborate clucking and exquisite condescension that get us nowhere. Attention should be paid to the serious underlying economic inequities, without the colorful surface distraction of concerned or judgmental prurience. Let’s abandon the fundamentally frothy question of who is wearing a ring. Young men need jobs so they can pay child support and contribute more meaningfully to the households they are living in. The real menace to America’s children is not single mothers, or unmarried or gay parents, but an economy that stokes an unconscionable divide between the rich and the not rich.