Facebook is the most sophisticated private surveillance network in the world. The breadth and depth of data they have on billions of individual humans is staggering. So they have the means to moderate their platform and mitigate content/persons they consider to be extremist. Instead of acting upon data they "own" using workers that they pay, they roped everyday people into doing the work for them.
The cynic in me is impressed: in one fell swoop they've wrung even more free labor from their users, turned them against each other so they don't unite, and have built something to point at when regulators start asking more pointed questions. It seems as effective as it is depraved.