This guy refuses to engage with the fact that the Zapatistas exist, an anarchist region with at least 300,000 people living under it, and also that Revolutionary Spain existed, an extremely successful example of anarchism in practice which resisted Nazi Germany better than any democratic nation in mainland Europe. I have pointed them out to him a few times now and he just keeps ignoring it, like an NPC in Westworld. It's more comfortable to deny reality when it lets you go on believing your existing beliefs. Admitting that you're wrong is hard.

By definition, socialism is a movement of, by, and for working people; distributing power democratically among the working class, and removing power from the wealthy and powerful. If a regime claims to be socialist while maintaining centralized, dictatorial power, then they have hijacked the movement to their own ends while coopting the language of it. Those regimes you mention were authoritarian because they failed to achieve socialism.