Voluntary and Communism

Kant demonstrates that there is a systematic relation between a psychological state, Autonomy, and a political structure, his Kingdom of Ends. Now, Marx and Engels make an analogous claim, i. e. between Voluntariness and Communism, but without any supporting argument. In other words, they do not explain why someone would freely choose Socialism over Capitalism, and, conversely, subsequent historical evidence seems to show that Communism can be totalitarian. It may be no coincidence that the fundamental principle of Kant's system--Reason--receives no attention in the German Ideology, and, perhaps, can receive no attention in an Empiricist "Material Method".