Most people think it's just kind of a free speech hellhole, but it's not, that's just the coat of paint the site took on/has always slightly had. Remnants of an idealized 1990's internet space where people thought everything would be free to use and free to access, and the storage would be infinite, ironically concocted by out-of-touch yuppies who didn't work on the pipes. In reality, free speech bullshit is always just a cover for admins to be able to enforce whatever totally inconsistent rules that they want without any form of repercussion, because obviously there are limits, even just legally, in terms of keeping the site up, and keeping it free from commercial spam, and having advertisers stay on. Most rules you can concoct have some sort of exception, or lack of clarity, or are too restrictive, so it really just falls down to some arbitrary decision as to what stays around and what doesn't.

With sites like 4chan, it isn't so much that "free speech" just inevitably leads to this tragedy of the commons where everyone becomes or is taken over by racists and incels, it's more that active decisions are made to turn these sites into shitholes by malignant actors, because sites like 4chan are the easiest targets, and have a kind of natural selection bias towards the type of people they want to recruit. They take advantage of this fact that "free speech" is obfuscating the actual moderation and enforcement of the site, and then use it to promote whatever ideologies they want, like a little internet meme terrarium, or maybe more of a virus cell culture. Then, this attracts other malignant actors, some of whom are even funded by different states, who work within the bounds of the site to advance it one step further, until you have a kind of horrible coalition of different ideas all stewing together.

Thus, most of the people who run the site nowadays are white supremacist dicks, funded by a hands-off japanese internet techbro libtertarian, and toy company "Good Smile".

Which is all kind of tragic, because, like that one guy said, it's responsible for a novel mathematical proof, the revival of a british indie rock band, the beginnings of anonymous, probably some other cool stuff I can't remember. Lots of early classic internet memes, of course. It's not all bad, really, it's just the lowest hanging fruit of web forum. Sometimes that's shitty, but then sometimes you get draw*** threads, where artists will go in and take low-pressure requests or concoct some sort of forum-game. Idealized, it's sort of like pub bathroom graffiti, or something. Which isn't really nefarious, is never serious, is sometimes charming, and very very occasionally is beautiful, useful, or novel.