“Speculators may do no harm as bubbles on a steady stream of enterprise,” John Maynard Keynes wrote in the twelfth chapter of The General Theory of Employment, Interest, and Money, the best thing ever written on speculative markets. “But the position is serious when enterprise becomes the bubble on a whirlpool of speculation. When the capital development of a country becomes a by-product of the activities of a casino, the job is likely to be ill-done.”

He wrote this in the 1930s, amid the economic wreckage of the Great Depression. The protracted slump was easily read as payback for the excesses of the previous decade, the great speculative mania of the 1920s. For a humane liberal like Keynes, the point of policy is to prevent manias and, failing that, to mitigate the inevitable fallout. That became the dominant view in mainstream economic and political circles for about four decades after the publication of his General Theory.

Even at the time, there were, of course, dissenters. Andrew Mellon, the US Treasury secretary who served under three Republican presidents from 1921 to 1932, famously advised Herbert Hoover to let the crash unfold in all its therapeutic splendor. “Liquidate labor, liquidate stocks, liquidate the farmers, liquidate real estate. Purge the rottenness out of the system,” he implored. “High costs of living and high living will come down. . . .  Enterprising people will pick up the wrecks from less competent people.” His words echoed those of Herbert Spencer, the brutal prophet of social Darwinism: “Cure can come only through affliction.” Or, as German finance minister Wolfgang Schäuble put it during the eurozone crisis, “Benevolence comes before dissoluteness.” When economic calamity hits, let it run its course, regardless of the human cost.