An easy disarm is "You are confusing privacy with secrecy. It is no secret what happens in the bathroom. It doesn't mean we are going to remove the doors because people still want privacy"
Still, I'm absolutely sure it's best to keep private stuff to oneself, and parties you trust. With understanding of full consequences of doing so. If one trusts Facebook, they'd better think why do they do so, as their trust may be misplaced.
I think one of problems is that when users post data they don't even think they send it to Facebook - they believe they send it to their friends there.