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?
Why hasn't anarchism been done already (on a large scale)? "It would have, but the tankies keep subverting revolutions and doing states, and they give a bad name to leftists which turns people away from anarchism," is a pretty convenient answer to that. Plus, by distancing themselves from us and from past revolutions, they can try to pass themselves off as "one of the good ones" while preserving an image of how they want things to be without having to defend any messiness of actually getting there. It's much simpler to write off projects entirely as not being genuine attempts because the bad people took charge than to actually study them and confront the complex problems they faced.