I pulled the fractions out of thin air, so I have no idea what they actually are.
But you have to do something about people refusing to enforce site policy, even if it's only on a small portion of the content.
For an extreme example (and to be clear I am not saying anything like this happened at CTH), if 99 posts out of 100 on subreddit fall within the rules, but that 1 post that doesn't is promoting killing everyone of a certain race, and the subreddit moderators refuse to do anything about that one post, then they 100% need to have something happen. And that doesn't change if it's 999 out of 1000, etc., either.
Now, it's unlikely that anything on CTH was at that level of toxic and hateful, but the same overall concept applies - they have to take care of posts that are against policy, even if they're a small minority. If not, it seems like getting quarantined or even removed completely is a reasonable course of action.