Johnson, Paul, Modern Times: A History of the World From the 1920s to the Year 2000 (English Edition).
Moreover, as the young Karl Popper correctly noted at the time, Freud’s attitude to scientific proof was very different to Einstein’s and more akin to Marx’s. Far from formulating his theories with a high degree of specific content which invited empirical testing and refutation, Freud made them all-embracing and difficult to test at all. And, like Marx’s followers, when evidence did turn up which appeared to refute them, he modified the theories to accommodate it. Thus the Freudian corpus of belief was subject to continual expansion and osmosis, like a religious system in its formative period. As one would expect, internal critics, like Jung, were treated as heretics; external ones, like Havelock Ellis, as infidels. Freud betrayed signs, in fact, of the twentieth-century messianic ideologue at his worst – namely, a persistent tendency to regard those who diverged from him as themselves unstable and in need of treatment. Thus Ellis’s disparagement of his scientific status was dismissed as ‘a highly sublimated form of resistance’. ‘My inclination’, he wrote to Jung just before their break, ‘is to treat those colleagues who offer resistance exactly as we treat patients in the same situation’. Two decades later, the notion of regarding dissent as a form of mental sickness, suitable for compulsory hospitalization, was to blossom in the Soviet Union into a new form of political repression.