1) well, they do remove some, and in order to not reveal how they identify them, they may not wish to talk all that much about it 2) it is baked into the model of free social media, not only that attention=advertising=money, but also that cost per user is very low (so they can keep the accounts free). If you add $1/user cost (to monitor with humans), for Facebook that would be billions more in cost. I don't know that a responsible social media company could be profitable; it may be that the very business model requires not policing it very well.