I don't think Facebook is built around private stuff, I think Facebook is built around sharing. I also recall Facebook managers stated many times that they see concept of privacy to be obsolete and harmful. Yes, of course, Facebook has privacy settings, since that vision is not yet accepted by most people, but the goal of it is sharing, not hiding (unlike webmail, for example) - the information on Facebook is by design supposed to be shared with other people. Of course, the set of these people can be different, but I think the easiest way to avoid publicizing private information is not publishing it on the site that is built for sharing and has always promoted sharing.
