I don't think there is much evidence for this 'Lich King' thesis that keeps coming up on HN. Destroying these platforms has likely positive effects.
I'm surprised people even find this intuitive. When you want to deprogram extremists in the real world you take them out of their radical communities, you don't put them into a nazi village or send them off to ISIS.
The real question is whether or not the shooter who frequents 8chan/2chan/voat/etc would have committed the shooting if they didn’t frequent extremist sites?
And to your real question: its nothing different than saying movies and video games inspires a CRAZY PERSON to do harm. I can read 'Mein Kampf' without building gas chambers, and I'm sure you can too.
It’s really ironic that given how much they bash it, the far right seem to be the ones who have taken postmodern nihilism the most seriously.
A separate site like Voat may be a bit different though. That is more of a closed ghetto for it.