It is hard enough on Facebook to have yourself organized so that family posts go to family only, and more public posts go public. And even then, how would you know? I don't think most Facebook users care that much about privacy and that is why Facebook can be so confusing about it. People who really care about privacy have many other options besides Facebook to communicate, and anybody who thinks of Facebook as anything more than a superficial social network that has a myriad of ways to invade your privacy should probably look into it, confusing as it is.
There are too many choices for customizing the privacy settings on Facebook. And there are a number of third parties who work with Facebook to extract personal information from users through apps and games. The privacy policies change often, and users often have to update their settings several times in a month to be protected from spam and unwanted ads.