Edit for clarity: I'm not asking why the Tankie/Anarchist grudge exist. I'm curious about what information sources - mentors, friends, books, TV, cultural osmosis, conveys that information to people. Where do individuals encounter this information and how does it become important to them. It's an anthropology question about a contemporary culture rather than a question about the history of leftism.
I've been thinking about this a bit lately. Newly minted Anarchists have to learn to hate Lenin and Stalin and whoever else they have a grudge against. They have to encounter some materials or teacher who teaches them "Yeah these guys, you have to hate these guys and it has to be super-personal like they kicked your dog. You have to be extremely angry about it and treat anyone who doesn't disavow them as though they're literally going to kill you."
Like there's some process of enculturation there, of being brought in to the culture of anarchism, and there's a process where anarchists learn this thing that all (most?) anarchists know and agree on.
Idk, just anthropology brain anthropologying. Cause like if someone or something didn't teach you this why would you care so much?
I wouldn't attribute the excessive internal violence to heads of state being in essence bad, I would attribute them to mistakes being made. Mistakes made under duress, sure, but still avoidable mistakes.
I'm not an expert on this but there are comparisons that can be made with figures like Julius Caesar and Napoleon, who were relatively favorable to the poor/proletarians, and used institutional power to seize control of the state to fend off reactionary forces. Lenin is less like these other two, but it is a tragic model that repeats in history.
Something else that plays into it is the proverbial person with a hammer to whom everything looks like a nail. When you're a revolutionary force, any entity you have conflict with instinctively feels counter-revolutionary.
We accept that representational bodies should include all demographics, ideally proportionally, because we recognize that someone from one demographic cannot understand the full experience and implications of the others, and therefore cannot speak for the others. The mechanism here is that people with power are going to use it in ways that benefit themselves, consciously or subconsciously; there is also going to be inequities based on how close people are to power. There are no fully equitable and considerate leaders. And this problem happens even in anarchist groups. I've personally noticed and commented on how avowed anarchists can end up reflexively "leading" things in all but name. A critique of democracy that came out of Occupy was that it is impossible for even a general assembly to represent everyone equally.
The solution is to have a mechanism in place from the beginning for how to devolve and disperse both formal power and informal power, down to a level that is deemed as acceptable.
Anyone who converts to a certain identity is prone to being sectarian at first, as a way of confirming their identity. The more history I've studied and the more I've experienced, the more nuanced many of my positions have become.