Because Stalin, or whatever? Yes, one of the worst mass murders the human race had ever seen. One of the champions of communism. Yes that helps show how communism is evil.
Saying that Stalin is one of the champions of communism is as meaningless as saying that Pinochet is a champion of capitalism. Definitions matter. Communism is the collective...
Communism is not a claim. It's a concept or an ideology. One could argue that it's a concept that does not work in reality, but a concept is not a claim.