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?
Probably in the minority with this one, my "grudge" originates from reading this: https://theanarchistlibrary.org/library/the-anarchist-faq-editorial-collective-an-anarchist-faq-full#toc562
And while it's much more toned down since then, it is still present as what you describe as "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." - which from my perspective is more like that the leaders of the USSR tended to resort to abuse of power in order to hold power and MLs are very vehement about the fact that these were no big deals or even were completely necessary to keep the project going, while, coming from anarchist circles, from my perspective these events change the nature of the project itself. This is mostly why i can relate to trots more - they are not afraid to call out what they perceive as self-serving use of power as mistakes, or even crimes.