I personally don't agree with the fact that Facebook has access to literally everything that we have online. At least that's what it seems like. However, that is why people should be careful about what they post on the internet because it stays online and anything has the potential to come back and bite someone in the ass.
A quick Google search for an old friend can bring up a Facebook page with a lot, or very little information. What people choose to allow others to see is in their control. It's known that what you put on the Internet will almost always be on the Internet forever, so every post you make on Facebook is of your choosing with the inherent risk that it will be public knowledge.
Facebook has yet to come into my house, turn on my computer and force me to post things online. When you do anything on a computer it is public in some sense of the word, and instead of worrying what Facebook is doing, I worry about what I am doing on the Internet in general. Facebook owns Facebook and determines its rules. It is a service you can decide not to use if you don't like the terms. If you want a communication to be private, write a letter, put a stamp on it, mail it, and hope the postman doesn't pry it open and read it.
It is not possible for Facebook to be encroaching on our privacy. People sign up for Facebook accounts knowing that others can see their information. On top of everything else there are settings that each individual can choose to use in order to show or not show certain information to others.