You can argue that they trust developers to be responsible. Having a user friendly and powerful SDK with tons of possible data points isn't inherently a bad thing. All of the features could be used in a responsible fashion, and FB thinks you're smart enough to do so.

I'm not entirely convinced of this personally, but it seems like a somewhat sound argument. I think that they know that it will inevitably be misused, and that they have enough incentive for allowing the misuse to continue.