Can we talk honestly about the value of two-parent families?

Liberals, can we talk about marriage?

No, not same-sex marriage. It's clear you strongly believe that should be a constitutional right, as do I. But there's another marriage discussion that you've been largely avoiding for, well, 50 years.

In March 1965, Daniel Patrick Moynihan sounded the alarm about the breakdown in marriage rates among African-Americans — and was excoriated by his fellow Democrats, who never quite forgave him for "blaming the victim." But it's impossible to read the Moynihan report today without thinking of the underlying conditions in Baltimore that gave rise to last week's riot:

"The fundamental problem, in which this is most clearly the case, is that of family structure. The evidence — not final, but powerfully persuasive — is that the Negro family in the urban ghettos is crumbling. A middle class group has managed to save itself, but for vast numbers of the unskilled, poorly educated city working class the fabric of conventional social relationships has all but disintegrated. … So long as this situation persists, the cycle of poverty and disadvantage will continue to repeat itself."

The situation didn't just persist. It got much worse. In 1963, 24 percent of black children were born out of wedlock, compared with 3 percent for whites. The share of white children born out of wedlock has since jumped to 29 percent. But the figure for blacks is now 72 percent.

Why does this matter? Moynihan summarized data showing children who grow up without fathers were likely to score lower on IQ tests, get held back a grade, drop out of high school and become juvenile offenders, all with damning consequences for employment and economic mobility. The impact of these disparities — and many others, particularly for physical and mental health and drug addiction — has spread as marriage rates have steadily declined.

Baltimore is one of the largest black-majority cities in the country, and the riots there were triggered by anger with the police over the death (now ruled a homicide) of Freddie Gray. But fueling the anger, as President Obama noted, is frustration with poverty and unemployment. There's no need to rehash the debate over whether single-parenthood causes poverty or vice versa. Each reinforces the other, and a new study by two Harvard professors identifies two-parent homes as one of five major factors in determining whether a community offers low- income children hope of economic mobility.

The reaction from the state senator representing Manhattan's wealthy Upper East Side was typical of the left: "This campaign seems laser-focused on shaming already struggling teen parents or, ludicrously, convincing teens not to get pregnant because really bad things will happen."

It shouldn't be controversial to tell young people that having a spouse or committed partner before having a child is likely to keep them out of poverty. Liberals, out of compassion, have gone too far in destigmatizing single motherhood — for other people's children, if not for their own. A little bit of stigma can have broad societal benefits. There is a world of difference between lovingly accepting a family member's out-of- wedlock birth and accepting it as a societal norm — and liberal leaders ought to say so.

Absent fathers, of course, are not the only problem afflicting Baltimore and other urban areas. The legacy of racism still hangs heavy over black communities, the decline in low-skill, middle-income jobs has made climbing out of poverty all the more difficult, and there is more that government can and should do improve economic opportunity in poor urban areas. None of these issues should be minimized. But since the Great Society, government efforts have produced such underwhelming results partly because it became sacrilege for Democrats to embrace what Moynihan, himself raised by a single mother during hard times, knew: Fathers play a critical role in a child's development.

"In an earlier age," Moynihan wrote in 1965, "the Carpenters, Wainrights, Weavers, Mercers, Farmers, Smiths acquired their names as well as their trades from their fathers and grandfathers. Children today still learn the patterns of work from their fathers even though they may no longer go into the same jobs." As the social scientist Lawrence Mead would later write, "What matters for success is less whether your father was rich or poor than whether you knew your father at all."

In today's more equal society, children can also learn patterns of work from their mothers. But one parent can only do so much on his or her own, and holding down a job while working full-time as a single parent can be impossible. Even graduating high school is difficult: Only 50 percent of teenage mothers obtain a high school diploma by age 22, compared with nearly 90 percent for non-teen moms, severely limiting their career options.

There may, however, be a middle ground. Although government can do little to persuade two people to stay together, there is an enormous amount it can do to help women prevent unwanted pregnancies. The latest development in birth control — intrauterine implants, known as long-lasting reversible contraceptives — offers the best protection against pregnancy. And over the long run, those devices are cheaper than the Pill. Those cost savings led South Carolina and Texas to change their Medicaid reimbursement rules to allow doctors to more easily order them, as Illinois and New York have also done.

If more states follow, more women will be in a better position to avoid unwanted pregnancies and have children when they are ready — and when, one hopes, the father is ready too.