4chan hasn't been "uncensored" for a long time. Over time most of the boards have become overgrown with obtuse and smothering posting rules, both written and unwritten (and new ones are often created out of whole cloth to suit the moment). Even the handful that are supposedly "anything goes" have been seriously reigned in. It's just that 4chan started out so open, and the modern web was gentrified so much faster, that even in its hobbled state the site seems like the wild west comparatively.