Guy Debord criticized the Soviet Union for creating a new class system. He still believed in Marxism, but didn't believe that the structure of the Soviet Union was able to create the conditions for communism.

Rosa Luxemburg certainly did but who cares about women in history am I right? /s

I don't think Marx ever condemned the word "authoritarian." Or said anything about a dictatorship of the proletariat becoming more unjust than a dictatorship of the bourgeoisie. That doesn't sound like anything he'd say.

Not according to "tankies" :D They love shiny boots holding a red flag. They just hate brown flags, but love a good boot-liking

Yup.