He might be the grandfather of activist government, but Keynes also said, in effect, that you should never think you have it covered, that you've abolished boom and bust.
This, in effect, is the argument that Hayek made against Keynes in the late 1920s and 1930s: he said the Fed caused the crash, by keeping interest rates too low and encouraging a lot of "malinvestment" - investment in projects or assets which were not economically worthwhile.