In my opinion this is an argument in favour of shutting Facebook (and every other large social network) down. This sort of work is damaging and abusive, and nobody should have to endure it just so we can have social networks. I understand there are some jobs in the world that need to deal with dark stuff (like law enforcement), but social networks just aren’t worth the human cost.
People would be less inclined to post this type of content to Facebook if it their account was very connected to their real identity, if they were 18+, and if there was meaningful punishment for making fake accounts or accounts with stolen identities.