Labor Day is an appropriate moment to reflect on a quiet catastrophe: the collapse, over two generations, of work for American men. During the past half-century, work rates for U.S. males spiraled relentlessly downward. America is now home to a vast army of jobless men who are no longer even looking for work—roughly seven million of them age 25 to 54, the traditional prime of working life.

This is arguably a crisis, but it is hardly ever discussed in the public square. Received wisdom holds that the U.S. is at or near “full...