As riots tore through Ferguson, Mo., and Baltimore this winter and spring, so did denunciations of a criminal-justice system that has placed a disproportionate number of black men behind bars. One widely aired theory holds that not only are racial disparities and mass incarceration patently unjust on their own terms, but they also result in, to quote Hillary Clinton in the first policy speech of her campaign, “missing husbands, missing fathers, missing brothers.”

The missing-men theory of family breakdown has the virtue of...