In dishonor of Castro, let us recall the two separate and distinct reasons why socialism is everywhere and always a human rights disaster:
Public Choice: the worst get on top and abuse power. Suppose that socialism really would improve the lives of the poor if only angels were in charge. The problem is, we don't have any such angels available. Even if we assume that socialism is perfect as an abstract economic system, nevertheless, socialism is not politically robust.
Price theory: the economic of socialism don't deliver the goods. Even if angels were in charge of government, socialism is not economically effective. Even if we could solve the purely political problems, the economic problems would remain. Even if we ignore the issues of political robustness, socialism fails as an abstract economic system.