> Facebook only knows what you are telling it, maybe don't announce your next bank robbery on your status update and you'll be alright

Right, because only criminals have something to hide. Maybe it's my generation, but I don't automatically trust Facebook (or the government for that matter, hello IRS) with the safety and security of my personal information. There are plenty of bad actors out there who can take my perfectly innocent movements and information and either ruin my life for the hell of it, or steal my identity and profit from it.

Facebook doesn't only know what you are telling it - Facebook knows a lot about you even if you don't have a Facebook account. They create "shadow profiles" of non-users through info about you your friends give to Facebook. They may also track non-users through Facebook beacons and "like" buttons placed on other sites.

Plus Facebook can very trivially figure out where you work without you telling them. Let's say a colleague lists they work at Initech. They then create a group called "co-workers" and add you to it. Now Facebook can do some very simple datamining and figure out you work at Initech. You betcha they do that.

Even if you don't have an account and browse the web like RMS, you still probably have a shadow profile unless you have no friends. If a friend gives the Facebook app permission to view it's phonebook (typical) and you are in it now Facebook knows and stores everything about you that's in your friend's phonebook - name, email, phone number, possibly home address, etc. This is one way it creates shadow profiles.

Facebook has face recognition software - need I say how much they can gather about you if your friends post pictures of you online?

Unless you installed AdBlock[Plus], uBlock[Origin], Disconnect, Ghostery, etc - then facebook knows about every page you've ever visited that had a "like button", whether you were logged in to facebook at the time or not, whether you've pressed the "like button" or not. Did you intend to tell them that? Your browser did anyway.

Also, they know everything your friends say about you (your pictures, which they feed into their face rec engine to find you even if you weren't tagged; and the exif data in those pictures often gives location data ...). And they have a shadow profile of you even if you never created a profile yourself.

Oh, and they have a copy of your phone contacts if you use the FB app or the whatsapp app.

All of this is documented by Facebook.

Facebook knows a lot more about you than what you are explicitly telling it.