Authoritarian communism is the only kind there is... it goes so much against the fundamental grain of human nature, that it has to be heavily enforced. Naturally once the government acquires a critical mass of power, it's all downhill from there.

The only communist "success story" is the PRC... they keep the communist moniker to rationalize their authoritarian control, while the workers get to live in a free market (that's free so long it directs wealth to the right bosses).

Most other communist regimes have collapsed under the weight of their own authoritarianism. Oh yeah, and the scale of their mass murder makes the holocaust look like a minor civil rights incident.