Why isn’t this matter at the center of policy discussions? There are at least three reasons. First, much of politics is less about what you are for than who you are against, as Jonathan Haidt, a New York University psychology professor, noted in his popular 2012 book “The Righteous Mind.” And intellectual and cultural elites lean to the left. So, quite simply, very few professors or journalists, and fewer still who want foundation grants, want to be seen as siding with social conservatives, even if the evidence leads that way.

Second, family breakup has hit minority communities the hardest. So even bringing up the issue risks being charged with racism, a potential career-killer. The experience of the late Sen. Daniel Patrick Moynihan is a cautionary tale: Moynihan, who had a doctorate in sociology, served in the Lyndon B. Johnson administration as an assistant secretary of labor and in 1965 published a paper titled “The Negro Family: The Case for National Action,” warning about the long-term risk that single-parent households pose for black communities. He was attacked bitterly, and his academic reputation was tarnished for decades.

Finally, there is no quick fix. Welfare reform beginning in the mid-1990s offered only modest marriage incentives and has been insufficient to change entrenched cultural practices. The change must come from long-term societal transformation on this subject, led by political, educational and entertainment elites, similar to the decades-long movements against racism, sexism—and smoking.