The question is how; perhaps through instances? User culture? Or even UX changes that make context harder to ignore and stupid shit sink to the bottom (against the Fluff Principle³)?
A simple and obvious solution is just to adopt the rules of communities on reddit that manage to maintain a average quality of content (askhistorians? r/science?), and building features that help with that (multireddits , so you will have different feeds for “fun” and “important”, or user tags) , reddit enhancement suite features could also be helpful.