The dumbest man says capitalism is the best possible economic system. This guy is right if he’s referring to global economic systems, because it’s been the only global economic system.
That is the real question. Communism is the main competition. We could try something in between like syndicalism, or some other version of socialism. But everything is theory because we’ve never tried a different system.
Communism could only work if everyone, seemingly under some hypnosis, all decided to discard wealth and possession and status and everything, all at once.
If any meaningful fraction of the population retains capitalism, the influence of personal gain would override, as it has in the past.
Yes and no it was an authoritarian communism system (there are many subtypes of communism and even more subtypes of socialism) also you could argue if they were communist at all depending where you standing on the autocratic-libertarian spectrum since libertarians/Anarchists would say that the point of communism is not that the state owns the means of the production but the people themselves.
Theoretically? It's already happened. It was the dominant economic system across the world for a while including during the colonization of north America. It was fudalists who conquered large parts of the world. International trade is older than capitalism.