4chan is moderated and the moderation is different on each board with the only real global moderation rule being "no illegal stuff". In addition to that the site does curate the content it shows you using an algorithm even though it is a very basic one (the thread with last reply goes to the top of the page and threads older then X are removed automatically.)

For example the qanon conspiracy nuts got moderated out of /pol/ for arguing in bad faith/just being too crazy to actually have any kind of conversation with and they fled to another board (8chan and later 8kun) that has even less moderation.