The much maligned fitting squad of BK the TA vs the entire population of his class is IMO neither the start nor the trigger for what followed.
From a practical standpoint, you're a professor. Perhaps you're getting bombarded with complaints about your TA. How much time would it take to have a sit down with each disgruntled student? A lot of time. How much time would it take to regrade the work and retrain the TA accordingly? There was no reason to think BK was violent, that he was homicidal nor, I'm guessing, any reason to think he couldn't handle a Q and A with students with diplomacy. It wasn't the set up that was troublesome; BK was troublesome. IMO he made it a stand off, he made it awkward, Betting BK doesn't like being challenged. So he quit trying, eventually giving out powderpuff grades. He's an all or nothing kind of guy IMO.
It was reasonable to address grading globally. It would have been reasonable to adjust his expectation, placate the students and his professor, in the spirit of growing into the position. He was in training and should've expected to be trained and retrained, as needed. Thousand ways he could have worked with the professor and the students, individually or collectively that could have... worked. He picked the one which showed how inflexible and untrainable he is, and IMO helped write the letter dismissing him.
For anyone shouldering guilt that they somehow pushed him over the edge, it only shows how caring they are, how capable of feeling remorse and taking responsibility, feelings most of can relate to, it's natural. You know who's probably not feeling any sense of remorse or responsibility? Yeah, the one who likely felt his outward life was a charade all along and decided one day to stop playing..
It was always just a matter of when.
JMO