The Snowden leaks revealed that Facebook has been passing off data, including private messages, to the government since at least 2013. This is unconstitutional under the 4th Amendment and therefore illegal (Marbury v Madison), but most people don't give a shit. I deleted Facebook a while ago because the normie memes were intolerable. Anyway, the data collection is part of a larger project by the NSA called Operation PRISM:
https://en.wikipedia.org/wiki/PRISM_(surveillance_program) Facebook has a long history of disrespecting peoples' privacy; it's all in the ToS. Boycott that shit.