Maybe to you and me, but we're not its target audience. Its target audience is other 8chan users, some of which might be just a step away from committing such atrocities themselves.
It's not just the manifesto. Places like 8chan are positive feedback generators for this kind of extremism. Every time one of these events happen it fuels the sort of unofficial contest to see who can be the next one, to be the next hero/martyr of the community. Easy access to guns is certainly a problem, but easy access to these radicalization factories is also a significant component that needs to be addressed.
Where did I claim it's the only thing needed to stop a person like that?
You gotta start somewhere. This is a nice and easy way to do that's completely within the reach of the tech community. There are no laws requiring that, just a sign of a good will.
If it were up to me, Cloudflare would block at least 30 other websites, starting with Gab. Unfortunately, it takes a shooting or two for them to realize that they have a problem with a client of theirs.
