Many people will downplay this, saying that the alt-righters on 4chan were only trolls, or were only a few people sockpuppeting to make it look like there were many, or that these people were already alt-right and that 4chan didn't actually influence anyone into it (and that 4chan's userbase merely cycled out to a set of new alt-right users), but I have to say that's all wrong. I was in several different online communities 2010-2018 of people who met through 4chan, and a startling number of people did actually adopt alt-right politics over this timeframe after I had first met them. I think people who downplay how common radicalization on 4chan was didn't have as clear of a picture as this experience gave me.