In my opinion, I don't think Facebook is the worst platform for privacy. This is because people give their opinion on Facebook, whether someone else likes it or not. However, it has privacy because someone can inbox someone else, which unless another person has your password, it cannot be read.
Their problems have more to do with communication from FB to users, than any security problems within the system.
And when you look at most of the complaints, it's from people posting things they wouldn't say face-to-face. So it serves as a reminder that, if you wouldn't say it to the person ... don't post it online.