...or other governments. And there's already precedent for getting around pesky things like the 4th amendment by simply buying your data from another country who has it.
If you are a Facebook user, there's a good chance you are manipulated by what you see there. Everyone denies it affects them (as I might, if I used Facebook), but it works. I trust the people who say they are vulnerable to manipulation - at least they give themselves a chance.
Facebook manipulates people you know (unless none of them use Facebook). Social media has dramatically changed some people I know well.
Facebook has enormous influence in the society you live in (perhaps depending on where you live), which affects you. Facebook has great power over the news people read, and Facebook is where many conspiracy theories spread, as examples.