Political discussion happens all the time on Hacker News, but you don't see many mass shooters from HN. Culture of the online communities matters a lot (and moderation). I don't think chans create gunmen per se, but they assist to radicalize antisocial young men.

I don't think anything is gained from political discussion on *chans. Free speech is important, and no company should be legally punished for providing these spaces, but that doesn't mean discouraging them from existing is wrong.