Facebook's utter failure to moderate itself (as documented many places but especially Careless People) is bigger than just a few weirdos advocating violence. The much more important piece is the fake news that says over and over again "group X did Y", "group X did Y", "group X, they're out there doing Y again". It's the echo chamber that magnifies and amplifies and reinforces untrue and half-true narratives, chasing engagement and fury and ad impressions with zero sense of civic responsibility.

It may be that no individual report is damaging enough to be censor-worthy, but the total effect is massively radicalizing, so that a huge group of people are primed to eventually interpret even true news stories in the maximally negative light and may even see their own eventual jump to violence as being justifiable self-defense given what they believe has preceded it.