It is a subject which has been discussed ad nauseum, and you would think there would be an understanding by now that Facebook is not private no matter how many privacy controls FB puts on. In some ways it may be better with respect to search, but its very nature will ensure it is never private — unless you have no friends while you’re there. Then you may have a chance of being semi-private on Facebook.
But realistically, you are probably speaking to others (or at minimum showing your identity through your profile) while on Facebook. This means you are not communicating with yourself alone but essentially with crowds. That in and of itself should make it obvious you are in public. It may only be a crowd of less than 20 or 50, but it’s still a bunch of folks who are listening and looking on. We understand this easily in face to face interactions, but somehow it’s forgotten on the Internet.
I’m not even going to discuss the marketing data that’s collected on you via Facebook. Oy.