I'm not convinced. Maybe a lot of people think of 4chan as a "cesspool" but I think it's actually quite functional with minimal moderation. They have a small volunteer staff to delete the absolute worst of the worst and let the rest roam free. The most radical thing they've ever done is made containment boards to keep the noise down.
I think the real problem is that sites like 4chan makes a tiny fraction of what Reddit does.
It works for 4chan's users or they wouldn't hang out there. But the level of moderation is a competitive feature. Users decide where to hang out based on the quality of discussion, and moderation has a direct effect on that (in both directions - too heavy-handed or too hands-off).
Also, in the end, the people who host a forum get to choose whether they really want to host a cesspool or not. If it's not working for them, they can shut it down, or maybe outsource moderation to Facebook or Disqus.
One of the big problems still is brigading. Even creating a containment board doesn't stop that, and I suspect having a board allows bad behavior to be legitimized through peer approval, and snowballs it. Also, it's so much easier to shitpost than generate quality content, just like its easier to lie than to debunk a lie.
I think the real problem is that sites like 4chan makes a tiny fraction of what Reddit does.