Since the grim days of the Great Depression, raisin farmers in California’s fabled San Joaquin Valley have raised their grapes under a food-regulatory regime that forces them to hand over a portion of their crop to the government, often without getting anything for it. The U.S. Supreme Court took a step, a big one, on Monday to give raisins something to dance about. Like many New Deal programs, raisin rationing was instituted under the foolish belief that manipulating the market to raise the price of raisins would make more money for the growers and improve the valley’s economic health. Hence,...