Hysteria erupted over President Donald Trump’s threats to level trade tariffs against particular countries. Both American and foreign critics blasted them as either counterproductive and suicidal or unfair, imperialistic and xenophobic. Certainly, tariffs are widely hated by doctrinaire economists. They complain that tariffs burden consumers with higher prices to protect weak domestic industries that, shielded from competition, will have no incentive to improve efficiency. Their ideal is “free” trade. Supposedly a free global market alone should adjudicate which particular industry in any country can produce the greatest good for the world’s consumers, whether defined by lower prices or better quality,...