Cuba as an example proves only one thing - that anything, no matter how bad, in small doses can appear successful. Any system, and perhaps Marxism moreso than capitalism, succumbs to the incompetence and corruption that grows exponentially with scale. We're experiencing it now, just as the USSR and Communist China did 30 years ago, leading to the collapse of their communist political structure. The idea that communism on the same scale as our current capitalist structure would be one one-millionth as functional and able to deliver widespread prosperity, is completely destroyed by the historical evidence.