It's a tough one. On one hand 8chan is a source for stupid values to sacralize, on the other it lessens social exclusion and staves off extremist behavior.
Anonymous internet message boards with a vague "large" audience are not substitutes for actual social interaction.
It's the same problem as Facebook and other social media: people present a curated persona, and ignore that they're only seeing everyone else's curated persona as well.
Ad marketing is already well into figuring out how to manufacture "authenticity".
It is a social interaction and it has effects of one albeit weak.
You can have bits of social satisfaction from hearing 'hello, how are you' from a store clerk or from watching people interact on TV. Definitely you can get it from getting responses to you anonymous or curated speach on the internet. Of course its not the same thing as honest interaction with your friend or loved one but it doesn't mean it does nothing for you.
Please notice they made people feel isolated by not passing a ball to them in a computer game.
Social circuits in the brain are so low level they can be activated by most superficial stimuli.
I dunno, at the same time people on these communities will try to one-up one another just to get attention. (this isn't limited to just 4/8chan btw, youtube "challenges" like tasering a dead rat or instagram things are other examples)
Do you understand that two things can be true at the same time even though they sound like they're opposite to one another? It's entirely reasonable to assume that places like that both prevent many people from falling further down a hole of exclusion but also push others further inside.
Their further fall into exclusion is stopped, because they are echo-chamber bubble that pushed them further into hate.
Social isolation does not make you extremist on itself - contact with extremists that recruit you make you extremist. Social isolation make you more vulnerable to extremists.
And how many mass murderers were not linked to any online forums or they were so crazy that they got ostracised even on the most extreme forums?
Three is just a number if you don't know the sample size. If it's 3 out of 3 million and the US had 600 mass murderers out per 300 million population then 8channer is twice as safe as average Joe. (Made up numbers to illustrate the math).
It's the same problem as Facebook and other social media: people present a curated persona, and ignore that they're only seeing everyone else's curated persona as well.
Ad marketing is already well into figuring out how to manufacture "authenticity".