I think the flaw is in the Marxist view of human nature itself.
It is to be beaten into submission. Perhaps there in lies the problem with Marxism.
Isn't it funny how in every attempted Communist society, an underground economy develops and the Communists are forced to either embrace (as they are attemting in China) it or attack its corrupting ways (as they did in the USSR).
By denying that it's existance is legitimate, the underground economy devolves into organized crime like behavior that is itself blamed for the failure of the Communist system...
Face it, Free Trade is ingrained in the human genetic sructure. Attempt to stop it are doomed to eventual failure.
Cuba will fall next. Castro can't live for ever.
Scott