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.
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.
A separate site like Voat may be a bit different though. That is more of a closed ghetto for it.