Communism is bad?

[~kitty~]

My dad and his friend try to tell me that Communism is bad. They say "it's bad because many millions die under the Communist rule, lots of their own people, and it's a God-denying type of government, and supports dictatorship." They talk about how corrupt it is, and how it's evil and there are no human rights in Communist countries.

Apparently, anyone who uses the word "Imperialism" in conversation, or in politics, is a Communist, or extreme leftist. Someone tell me exactly what this is all about?