At risk of going into tin foil hat territory, all of this right wing radicalisation does kind of remind of me of all the offence taken at The Last Jedi, often to the point of harassing the actors, and how it turns out that was all just a few fringe loonies being egged on by bots and paid shills. Not to mention, the influence they had in the 2016 US election. It makes me very strongly suspect the cause of this recent string of shootings is yet more bots and shills. In which case, maybe it's not just gun control but also strong regulation of social media that's called for. In fact, you could even argue that social media in its current state is a threat to national security.
Of course, I haven't the foggiest of what specifically should be done or how we should go about. Ah well, 'tis one of the great conundrums of our day, to be sure.