Communism is utopia. It could only be achieved in small, closed societies. Communism relies on people to be truly altruistic, with compassion, super humane in a sense. And this can only be achieved if a society would have no economical or cultural problems whatsoever, internal or external. People should be willing to do "greater good" for the whole society and not for themselves but this can only be done if all the people in such society are more or less equal in all terms, so the uniqueness of an individual has to be removed completely, which is practically impossible.