Such freedom seems so essential to Internet culture that, in my opinion, it must be protected.
Can you provide an example of something valuable you found on 4chan/8chan that could not be found on a site with less "vileness"?
Ok admittedly, this was 10 years ago and 4chan was a much different place (as was the internet at large). I was younger and spent a lot of (read: too much) time on 4chan back then.
At the very beginning of Minecraft, before it was even a thing, Notch would post on /v/ about it almost daily - incorporating changes/suggestions/criticisms people would fling at him anonymously and randomly. No one thought it would be huge - it was just fun. And Notch was so receptive.
I can't help but think his current Alt-Right views may have been influenced by his exposure to 4chan, but in those days it wasn't as crazy as it is now.
I have a 4 year old daughter now who LOVES Minecraft. And personally, it's been valuable to me, and I am utterly convinced that had Minecraft not been developed in its earliest days on 4chan, it might not have gotten to where it is today.
*Small shoutout also to Katawa Shojo - also made with lots of input from 4chan, which turned out to be quite a compleling VN game.
What has 4chan done lately that is valuable? That I couldn't tell you.
For example, couldn't Notch post on Reddit every day, incorporating changes/suggestions/criticisms people would fling at him anonymously and randomly?
Is there something about 4chan/8chan that is intrinsically better for building Minecraft that isn't available anywhere else?
I'm convinced the initial randomness/anonymous feedback/chaos of that initial period helped grow the spark from the ember that split off of Infiniminer.
There is something creative in the chaos of 4chan - just look a greentexts. 99% of them are absolutely terrible. But the occasional gem catches on and made viral on the larger, less vile sites.
Also, I can't believe I forgot about Caturday. That started on 4chan as well. (also 10+ years ago).
I get both from elsewhere, but they originate on 4chan.
The experience I found on 4chan is pretty unique, and I don't know how well I can describe it, but I'm really glad that there was somewhere like it.
That said, 4chan's culture definitely started to decline around 2014~2015ish, around the time of Gamergate and the Trump campaign. Whenever 4chan's "hub of vileness" reputation starts getting really public in the news, the result is that a bunch of new people who think "hey, that sounds like exactly my jam!" start flooding in. And those two events both drew a huge amount of attention to 4chan, and not the kind of attention that brings good people. (It didn't help that a huge chunk of the old userbase fled around the time of Gamergate due to controversies about it on the site itself.) /pol/ was always a little leaky, but it started to get a lot worse around that time. Not to mention that /tg/ itself was already on the decline because of the positive reputation it had gained elsewhere on the Internet as various stories originally found on it were posted elsewhere, and so it increasingly became full of people who wanted to hear those kinds of stories but weren't actually RPG players themselves. There's a lot less positive to recommend the site these days, and a lot more negative.
That is a polite way of describing anti-Semitism and conspiracy theories such as Q-Anon.