The thing that frustrated me with Lance Armstrong over so many years was the smirk on his face when asked whether he used drugs, and he would reply, "Hey, I passed the test, isn't that good enough for people to stop asking?"
I suspect Facebook is falling in that same boat - technically following rules so they can answer questions the right way. But we're not seeing the smirks on their faces as they give that answer.
Besides Facebook denial and the complete lack of empirical evidence, what are you looking for? Why do people keep talking about "this one time it maybe happened", when it should be happening to everyone all the time, if it's happening at all?
I suspect Facebook is falling in that same boat - technically following rules so they can answer questions the right way. But we're not seeing the smirks on their faces as they give that answer.