> Imagine a world where you could say "Communism is bad" with the same impunity as you can say "Naziism is bad"...

I can imagine a world where "Communism", like "Naziism", was a label for a single system of government implemented by a single group of people in one time and place in history, with no theoretical model (and prior practical advocacy) that shared the same name but had substantial differences.

OTOH, that world is very much different from the real world, so when one wants to criticize one of the things called Communism, one needs to be careful in identifying which it is, since there are multiple of them, and they have different traits.