I don't think Marxism was Popper's side act, particularly later in life (The Open Society And Its Enemies, The Poverty Of Historicism). Marxism and Freudianism were targets of Popper's because they appropriate the language of science for what he argued were in fact non-sciences.
It's important to remember that in the '20s, Marxism was presented as a scientific theory, that it described a logical, teleological process by which human society could be perfected. This was the Popper's later great white whale. Ask George Soros!
It's important to remember that in the '20s, Marxism was presented as a scientific theory, that it described a logical, teleological process by which human society could be perfected. This was the Popper's later great white whale. Ask George Soros!