Online privacy. People actually want it. They expect it. It does not matter what your terms of service has buried in the small text. People really do not want all their information spread out to whomever wants to buy it through ad servers.
Facebook is different that many online privacy issues because people but in lots of details into the Facebook profiles. Plus their online posts can reveal plenty about themselves.
Facebook now says they will make their privacy settings easier to use. the current set up obviously does not work for many people simply because they do not know how to use it. Plus some people would never expect all that information to be available. Hopefully the new facebook privacy settings will keep everyone happy and secure.