Facebook's main income is advertising not data. They collect data yes; but more so they can direct adverts at you than for selling it. Additionally Facebook does not 'sell' information unless you have allowed it, they do however use it for the targeted adverts - the owners of the adverts never see the data. Governments can request data and if it is a lawful request then it is supplied - they cannot buy it.
FB uses your personal data to generate personalized ads. That's the idea. For me it doesn't work. I liked Call Of Duty, Metro, and some other stuff on Facebook. All i get is ads from Vodafone and other mobile providers and many other crap I am NOT interested in. Instead of ads for FPS or at least game ads. Nothing. The algorhythm doesn't work. Google is not able to place personalized ads and FB fails too. It's a nice idea - if it works
About the "lawful" reasons.. erm. The past weeks have shown that they don't need "lawful" reasons to sniff the internet traffic. NSA, GCHQ & co SAY they have. I still don't trust them...
Targeted advertising will always have inaccuracies for the majority of people it works though which is why it generates billions in income for companies.
You are confusing me saying that Facebook doesn't sell data to governments with something on an entirely different level and different subject. The original comment was that Facebook sold data to governments; I was responding to that - not addressing data security and governments.