[chmullig]

I interned at Facebook a few years ago, so I'll speculate with an ounce of information.

There's a lot of openness, including around issues like this, at the company. There's weekly all hands meetings, where a developer could directly ask Mark about his opinion on a feature like this. The user experience, including creepiness, was almost certainly discussed. They may have misjudged in this case, but that's fallibility, not because it was ignored.