1) USSR, China, DPRK, Cuba, Nicaragua, Venezuela, Vietnam, Laos, Yugoslavia, Burkina Faso, Bolivia, Mongolia, and to some extent the anti-colonial movements in Africa, Latin America, the Middle East, etc.

2) Marxists don’t advocate utopianism (Read “Socialism: Utopian and Scientific” by Engels)

3) Socialism already exists, which is why I proposing learning from all the previous successful proletarian revolutions, studying Marxist theory, and applying it to our unique conditions. I’m not proposing anything out of the ordinary.

Other:

There’s no such thing as human nature. There is only human behavior, which depends on material conditions.

Since you mentioned authoritarianism, you have to read “On Authority” by Engels before going any further (this will answer all your questions).

The last thing I’ll mention is that, as I alluded to, most of what we are told about Marxist, socialism, and communism in the West is false. I have compiled an extensive list of educational resources if you’re interested:

https://linktr.ee/MatthewJohn