I wouldn't put this on the users' lack of clarity as much as I would blame Facebook for changing the course of it's features so much so that this is now happening to people. People were using the site as it was once intended and we can't blame them for being infuriated when the logic behind that usage changes. To me it's no different than Quora deciding to make all of your posts public without the chance to opt-in, except because of Facebook's privacy settings mess, it isn't easily reversible without severely crippling the content you've posted over the entirety of your account's lifespan.