4chan and 8chan are cancers upon the internet. The sites themselves and their community members spew toxicity, hate, cynicism, and revulsion wherever they turn up. They revel in trolling, harassment, and offense for the sake of offense. This, as recent events demonstrate, often extends further into deep-seated hatred and racism. I don't know if it's an intrinsic side effect of the 100% anonymous culture or just just the way they developed over time, but there's no denying that they serve as a perfect breeding ground for this kind of indoctrination and degeneration.
They're perfect feedback loops - the more time one spends in such places, the more strongly the mindsets they proclaim become rooted and the harder it is to break away. People go in feeling alienated and rejected and stay stuck there, finding a perverse connection in their inability to connect and interact with the rest of society in a positive manner. As a result of fixating on the things that set them apart and consuming endless torrents of content from people similarly afflicted, it makes it even harder for them to escape the feedback loop. Mental illness is rampant among the users there, and instead of people afflicted with it being helped or guided into acceptable patterns of interaction, they're mocked or worse yet praised for the negative behavior they exhibit.
I've seen this happen to several friends first-hand. One of the most dangerous and destructive things that I've noticed is a disconnection between ideas and reality that comes out of a broken concept of "irony." A common claim is that people started these communities as places where they would "ironically" pretend to be racist or mentally ill, and as a result they attracted actually racist and mentally ill people who ended up taking over the community from within. I think things go a step further: that people who "ironically" take part in hate speech, homophobia, and other bigoted belief systems end up slipping into believing them themselves. Or rather, the line between irony and reality itself dissolves over time after constant exposure, often at the exclusion of all else.
I don't have any ideas for solutions to the problems that these kinds of communities create. Their very design makes eliminating the issues or cutting out bad actors completely next to impossible, and no amount of cleanup work after the fact is going to eliminate what is clearly a deeply-rooted and persistent system. Any attempts to exemplify the sickness of their community will be seen as attacks and just make their beliefs deeper.