I'll direct you towards my comment elsewhere, copied here:

"Not real communism" has 2 flavors.

1. Western "leftist" edition, claiming all existing socialist states never achieved even socialism

2. Marxist edition, pointing out that socialism is a transition to communism, and that communism has not been achieved yet.

The latter is correct, but often gets mistaken for the former, which results in rhetorical gotchas by liberal debatelords.

In other words, communists have killed people and made mistakes, but have played an overwhelmingly positive role. Further, most of the people killed by the communists have been fascists, capitalists, landlords, etc.