Progress cannot happen in society without good & bad ideas freely propagating, and individual decisions to buy into them or not. Every significant cultural movement stems from a counter-cultural uprising, and these sorts of things would be swept up in the "vetting".
Again, it's 4chan with more rules. Anybody can post anything. It's not a place of fact or truth. It's of people sharing their lives, thoughts, hobbies, opinions, notices, likes & dislikes, etc. Some extremist $SIDE-wing Facebook channel is simply posting such things. It's not an official channel for trustworthy news, it's users being social, whether that user is Aunt Flo or CNN.
The core problem is that people think it's a "trustworthy" information platform (and Zuckerberg wants that trust for more customer buy-in). It's not. And it won't be, unless you remove the core personal family & friends social aspect of it.