During the writing of his biography of Mountbatten, Philip Ziegler posted a little reminder to himself above his desk: “Despite everything, he was a great man.” Unfortunately for the anecdote, in Mountbatten’s case the reminder was untrue. It would have made for a much better story had the note been written by Lord Robert Skidelsky to guide him as he chronicled the life of John Maynard Keynes.

Keynes was one of the most influential thinkers of our century, and his influence has been almost entirely bad. Since time immemorial, governments have debased their currency, misappropriated their people’s wealth, and diverted the proceeds from productive investment to garish monuments to themselves. It was Keynes who supplied governments with arguments—and since Keynes was Keynes, brilliant arguments—to justify this outrageous conduct. If John Maynard Keynes had never lived, the Western world might...