That's a concern leveled elsewhere in this thread: that you go to 4chan to discuss music or retro video games, and are one click away from an absolute hive of poisonous extremists.
The answer is structuring society, socialization, and culture in a way that doesn't disenfranchise people or leave them feeling helpless enough to turn to extremism, hate, and violence.
But that requires empathy and effort, things often in short supply.
People only go down the dark paths that lead to 8chan et al when the avenues to belonging they were presented with by their parents and by default failed them.