As I said in another comment below

‘Containment’ doesn’t work. That was the reason /pol/ was created, but all that did was rapidly radicalize the userbase, which then spread back to the other boards.

Giving them a dedicated space to radicalize people doesn’t mean that the people who get radicalized will never leave that space. Because not only did it spread back to the other boards, it spread outside 4chan. The rise of the alt-right can be directly traced back to Steve Bannon recognizing 4chan as the ideal target to start radicalizing users there. And now look at where the alt-right is today. It’s not an exaggeration to say that this is a large part of how we got Trump.