“Family disruption is not a random event,” wrote Sara McLanahan of Princeton, Laura Tach of Cornell and Daniel Schneider of the University of California, Berkeley, in a study assessing efforts to disentangle the effect of selection from that of family structure. “The characteristics that cause father absence are likely to affect child well-being through other pathways.”

Then, of course, there is the issue of resources. Families headed by single mothers are poorer.

Studies in Britain suggest that children in single-parent homes suffer because they are poor, or because of the shortcomings of their parents — not because their parents do not live together.

Given the evidence, marriage promotion might even backfire. Encouraging a mother to stay with a father who deals in drugs, can’t hold a job and beats her can actually lead to worse problems for the children, according to Sara R. Jaffee of the University of Pennsylvania.

But the strongest case against a policy to deliver strong marriages and stable families is that the government has no clue how to do that.

Remember the Healthy Marriage Initiative? When MDRC, the policy evaluation organization, performed a careful evaluation of its program of marriage education for low-income married couples who had or were expecting children, it had to conclude that it “did not lead more couples to stay together.”

Similarly, researchers at the National Center for Family and Marriage Research at Bowling Green State University in Ohio concluded in 2014 that there was little to show for the $600 million spent on the Healthy Marriage Initiative since 2001. Notably, the divorce rate had not budged and the marriage rate continued to decline.