Perhaps some of the people you’re referring to are otherwise unemployable for related reasons—by giving them paid work, FB could do public good.

Of course, that is assuming they truly have “no problems dealing with” that content, and won’t be triggered by it to do something terrible in real life. Not sure if mental health care is/can be advanced enough to tell precisely.

Like clinical psycopaths? I mean I guess psychopaths don't have to be bad persons.

I read a story about a cop that watched all seized child pornography to catalogize the victims and perpetrators. It probably requires a certain kind of person.