You deploy an AI to moderate, and it lets you cut your moderation workforce by 80%. Maybe you're a generous person, so you cut by 50% instead and the remaining moderators aren't as overworked anymore. (Nobody's going to actually do this, but hey, let's be idealistic.)
Costs are down, things are more efficient. Great! But there's a little problem:
Before, 90% of the posts your moderators looked at were mundane stuff. They'd stare at it for a moment, evaluate the context, and go 'yeah this is a death threat, suspend account.'
Now all the moderators see is stuff that got past the AI or is hard to classify. Dead bodies, CSAM, racist dogwhistle screeds, or the kind of mentally unhinged multi-paragraph angry rants that get an account shadowbanned on places like HN. Efficiency turns the moderator's job from 'fairly easy with occasional moments of true horror' into 'a nonstop parade of humanity's worst impulses, in front of my face, 40 hours a week'.