“The whole aim of practical politics,” wrote H.L. Mencken, “is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary.” Last year’s hobgoblin was swine flu. The President’s Council of Advisors on Science and Technology warned of as many as 90,000 excess flu deaths, and the federal government declared two national emergencies. Yet, with the U.S. flu season ending, the Centers for Disease Control and Prevention estimate we’ve had perhaps a third the usual number of flu deaths. This year’s hobgoblin is Toyota. You...