Earlier quoted context omitted.
You need to make a distinction between 8chan as a website and /pol/ board. Imageboards are just places for unmoderated and free discussions, the topics are up to users (especially on 8chan, where they can even create their own boards, which is not possible on 4chan). Most of the discussions there are innocent in nature, it's always the same few boards which create shit like this.
Yeah, and part of the problem is that policy allows the bad boards to stick around so they multiply. In practice the bad policy means it doesn't matter how many good boards there are because there's a board next door hosting child porn or something.
It's the same reason why Reddit administrators hasn't deleted /r/the_donald yet, despite many of it's users breaking Reddit rules. It's hard to draw the line where it's acceptable to ban a whole community with "safe topic", because majority of posters are breaking the rules / law.