Facebook didn’t generate the objectionable content. They created a mechanism for people to communicate with one another, like radio did a century earlier. Asking Facebook to check to make sure people don’t missuse the platform is like asking radio manufacturers make sure equipment doesn’t fall into the hands of evidoers.
What would you have had Facebook do, specifically? What practical steps are you wanting them to have taken? Could those steps be reasonably taken for every country in the world?