[Quote the essential paragraph; "The rationale is simple: they have proven themselves to be lawless and that lawlessness has caused multiple tragic deaths. Even if 8chan may not have violated the letter of the law in refusing to moderate their hate-filled community, they have created an environment that revels in violating its spirit."]
In the case of the El Paso shooting, the suspected terrorist gunman appears to have been inspired by the forum website known as 8chan.
Anything can inspire a lunatic, John Hinckley Jr's assassination attempt of Ronald Reagan was an attempt to impress Jodie Foster.
He could have easily been inspired by a movie or a previous shooting, since these shootings are copycat killings. It's the new trendy way of getting their 15 minutes of fame. These things didn't become a regular occurrence until the social media era.
This does absolutely nothing to prevent extremism and radicalization. Reddit and other forums have tried the exact same thing with banning subreddits and the users just migrate or create other sites.
In fact, it makes preventing shooting/bombings even harder because now they don't have a central place to track and monitor the people doing them.
You are correct as it does nothing to help, but as for a business they are choosing to separate themselves from what they feel in inherently wrong. I applaud them in that aspect. Cloudflare not being a host of such content like you mentioned at reddit, they do have the ability to say "we think you went to far as we feel our services are not best aligned with the content that you choose to allow on uch an ethical level"
This really doesn't make it that much harder as the content still remains with 8chan and the content still will exist with no interuption. The services however will most likely change of what 8chan is using.. more or less cloudflare has set its own embargo against 8chan.