For an authoritarian government to work long term they have to be the highest power. This is why the Soviets worked so hard to destroy the church as well as the concept of family, people who value god or family above the government are a threat. In effect the government has to become god.
Is this true? I always found it strange that the Kremlin literally has five churches inside of it... I mean Communism and Christianity have a surprising amount of commonality. https://en.wikipedia.org/wiki/Christian_communism
As for persecution of clergy is true, I suppose it depends if you count mass murder, torture, and shutting down churches as persecution
https://en.wikipedia.org/wiki/Anti-religious_campaign_during...