Good intentions are over-rated. Franklin Delano Roosevelt's New Deal, for instance, has been hailed for its lofty goals of reforming the American economy and helping the under-privileged. Yet mounting evidence, developed by dozens of economists across the country, shows that the New Deal prolonged joblessness for millions, and black people were especially hard hit. The flagship of the New Deal was the National Industrial Recovery Act, passed in June 1933. It authorized the president to issue executive orders establishing some 700 industrial cartels, which restricted output and forced wages and prices above market levels. The minimum wage regulations made it...