Dennis Robertson (1928), famous Cambridge economist that even though was close to Keynes (at least before the General Theory) remained thoroughly anti-Keynesian, said regarding cranks that:
"those who have Found the Light about Money take up their pens and write, with a conviction, a persistence and a devotion otherwise only found among the disciples of a new religion. It is easy to scoff at these productions: it is not so easy always to see exactly where they go wrong. It is natural that practical bankers, vaguely conscious that the projects of monetary cranks are dangerous to society, should cling in self-defence to the solid rock, or what they believe to be so, of tradition and accepted practice. But it is not open to the detached student of economics to take refuge from dangerous innovation in blind conservatism."I have a more sympathetic view than Robertson about the cranks, which tend to provide critiques of the mainstream without being able to build coherent alternatives. Cranks usually liked paper currencies during the Gold Standard (like Silvio Gesell), and were concerned with the practical problems of unemployment (like William Trufant Foster). More often than not they understood that money was both endogenous, and that it had real effects on the economy, something that still puzzles the mainstream.
Keynes (in the GT) was wrong in putting Gesell, and Major Douglas (another monetary cranck) on the same group with Marx. From a history of economic ideas, while Marx is grounded on classical political economy, even if he is critical of several aspects of Smith and Ricardo, Gesell and Douglas were not grounded on either the surplus approach (of the classicals) or the marginalist approach, even if they both had elements of the latter.