For a real life example, there is a group of people that collect Facebook posts and process them through a ML filter which judges if the post contains hate spee

For a real life example, there is a group of people that collect Facebook posts and process them through a ML filter which judges if the post contains hate speech, and if it does, it reports the post to the police, supposedly after manual review. Does this processing comply with GDPR? I'm pretty sure none of the people would allow this processing to take place if they were asked for permission.