Unfortunately if it's cool to hate a group of people as 'degenerate' this sort of thing ends up happening sooner or later.
Not to mention, "degenerate" is a common Nazi dogwhistle, and people who think it's cute to use it should probably be asked to explain themselves.
We may never know who perpetrated the chlorine attack at MFF and why they did it, but if we run with one of the popular hypotheses, I think it shows the importance of taking stochastic terrorism and the like seriously, because it always starts with dehumanizing rhetoric being repeated often enough to be eventually taken for granted.
As for some of the other things y'all brought up, yes, I think more people could absolutely stand to be coached on how to handle trolls and critics better, but Fallowfox is right that we need to be wary of treating trolls like the weather, and effectively blaming bullying victims for making themselves "attractive" to trolls. (Does that argument sound familiar, perhaps?)
Kimber in particular also flagged how the fandom is sometimes too tolerant and forgiving for its own good, and too focused on impression management and circling the wagons, to the point where toxic and disruptive behavior and dangerous and hurtful people either get a pass, or are otherwise allowed to slip through the cracks. MaelstromEyre is right that "but my autism" can sometimes become a get-out-of-jail card that ends up hurting both the individual who's learned to over-rely on that card and everyone else around them. (At the same time, we still need to be appropriately empathetic and patient with folks who have certain struggles or issues, but are doing their absolute best to manage them.)
From there, the question of how to regulate social media is a huge, complicated question. Yes,
some form of regulation is necessary and important for the safety and satisfaction of all, but how to go about that is obviously easier said than done. You've got to figure out how to create rules and standards that can't readily be misinterpreted, distorted, abused, or over-extended, and you've also got to consider how social media platforms will be inclined to create rules and policies that ultimately favor them, theirs, and their preferred status quo.