Sarcastic reaction..nothing else...
4chan is really nothing like that, at most you can say they are edgy kids larping as nazis, neo nazis but you will find based kikes btfo'ing them, most of them are just your average joe but that is your /pol/ board.
4chan has different boards assume it like different 'mini-forums' within a forum dedicated to separate topics, like /pol/ is for politically incorrect so you will find racism, bigotry and everything which may or may not get you in trouble for speaking in public.
There are good boards where you aren't allowed to do that, /int/ is pretty cozy, /g/ is good for learning, /k/ for guns is interesting but don't browse much. Once in a while check /g/, /v/ or /pol/ and sometimes /int/...there are many other boards dedicated to nsfw topics, travel and so on...
Most of the infamy it got was due to /b/ and /pol/.
At the end it's a platform just like this forum or any other, since people are mostly anonymous they get a bit more edgier and I can't really deny illegal part since few of the things are borderline illegal...so yeah. But it's not your dark web...