(I told myself to avoid political post and yet here we are)

Not just the USSR, but also China, North Korea, Yugoslavia, Albania, Cuba, Venezuela, Cambodia and Vietnam. They all turned into vicious, brutal dictatorships. It also happened in the shadow the Spanish Civil War (read Orwell on how that went). And the USSR did not just turn into an totalitarian state, it immediately became one. Lenin immediately started to wipe out class enemies, Trotsky immediately turned into a bloodhound that eventually turned against their own (Kronstadt). Stalin was just the logical consequence and the dead state after the Khrushchev Thaw was by no means the result of external influence. The system was dead, because it had nowhere to go. The moment someone tried to move it, it fell apart so quickly that the British MI6 believed it to be a communist plot (which is more telling about the MI6 than the USSR).

Looking at the world and history, Marxism is either (a) a fancy, but unrealistic idea, (b) so unstable that a small number of people can fully and permanently derail its course or (c) it cannot be implemented without piles of bodies and violent enforcement of obedience. Probably all three are true.

Sadly, the European countries currently put their social systems into a great experiment and it is unclear how that might end.