Seems to me that keeping the labor cost reasonable isn't really that difficult. The only real problem is concealing the process well enough that it doesn't provoke outrage. Understand as you read what follows and the hairs on your neck stand up that this is --- after enough layers of BS are applied --- very close to what will evolve.

Just yesterday we read about how Facebook 'helps' marketers 'track when people were feeling overwhelmed, worthless or insecure' [1]. Focusing on people that exhibit this frequently, particularly if they're being bullied, would catch a bunch of these online suicide cases without squandering labor on everyone else.

Then all you need to do is invent enough euphemisms to enable a degree of profiling; the rape streams that go unreported for days are almost always gangbangers. Should be a trivial job to factor that group out, by their grammar alone.

There you go; the chronically depressed types and the gangbangers account for probably 95% of the headline making cases Facebook has to worry about. Focus a small workforce on those two groups (and possibly a few others; extremists, etc.) and Bob's your uncle.

[1] http://www.moneyandmentalhealth.org/facebook-mental-health/