Growing up in Michigan in the heyday of the United Auto Workers, I long assumed that labor unions were part of the natural order of things.

That's no longer clear. Last month the Labor Department reported that private-sector unions lost 834,000 members last year and now represent only 7.2 percent of private-sector employees. That's down from the all-time peak of 36 percent in 1953 and '54.

But union membership is still growing in the public sector. Last year 37.4 percent of public-sector employees were union members. That percentage was down near zero in the 1950s. For the first time in history, a majority of union members are government employees.

In my view, the outlook for both private- and public-sector unionism is problematic.

Private-sector unionism is...