Facebook has collected massive amounts of personal data through our online habits (including advertising networks that track the web sites we visit), our posts on Facebook, the posts we like and share, the sites we log in to using our FB log in ID for access, and possibly scanning even our text messages on smart phones (their Facebook app gets permission to do so), and the details of our travel (via the Facebook apps use of location data).
No one knows the algorithms that FB applies to discern patterns about us. No one knows how much data FB has collected on each of us. No one knows how this information is stored. No one knows who has access to this data.
All we know is that Facebook is the largest, friction-less platform for the dissemination of propaganda. One company has the ability to rule the world.