You underestimate the depths of depravity of these discussion boards. 8chan is (probably) already strongly monitored due to the proliferation of child porn throughout the site.
Its not that they've messed up recently. They've messed up repeatedly and consistently over the past years. Child porn, hate speech, the works. Its all there. FBI knows this, but they are only allowed to move in when the laws provide them the opportunity to move. They can't shut down the site, they can only monitor these anonymous posters (who are probably safe behind many layers of proxies) and maybe try to figure out the troll vs the serious ones.
As I stated before: the laws have to change before the status quo changes. Its that simple. No one will support the FBI raiding private websites on free-speech grounds however, outside of specially select circumstances like child porn.
I mean, do you want to talk to white supremacists? Just go to Stormfront or Daily Stormer. Yeah, FBI probably actively monitors them too. There's an entire dark-net out there that the mainstream stays away from.
Or what, do you really expect the dark-net to just disappear because of one or two incidents? Daily Stormer was banned from Cloudflare a long time ago, they just found new hosts and carried on business as usual.
I'm glad Cloudflare is doing what they can to stop this filth. But Cloudflare is just a small part of the internet, and a real legal solution needs to be created if we really want to fight them. This is a bigger problem than Cloudflare can handle.
ISPs/websites in the US are required to proactively report child abuse to NCMEC, so they don’t need to be “strongly monitored” unless of course they’re not complying.