As I have said, smart people often fall into the trap of believing this. But it is not true: for many terrible things were done in the name of communism; but communism was an explicitly internationalist movement. Fascism is an explicitly nationalist movement.
It is worth pointing out that during the Nazi’s rise to power, they fought against the communists. Fascism and communism are both cruel, but they are very different in terms of their core philosophy and assumptions.
This is why I have such sympathy for the libertarians; their philosophy serves as a safeguard against the evils of both nationalist fascism and internationalist communism.