It's anecdotal, but when I stay off FB I feel better about life. When I compulsively browse for hours, I feel terrible about myself, my friends, and the state of the world.
Intriguingly, Facebook has started doing sentiment analysis, putting them at risk of discovering with statistical rigor that their product causes depression. If so, their position right now is no different from the tobacco companies, in that they know that they're making their users sick.
Not sure if it's a good indicator but suicide rates seem to have jumped massively in the last 10-15 years.
Sometimes you're feeling bad about the world because the world's relationship with you is crummy, not because you're broken your self.
Realistically, if they changed their jobs they'd probably be more happy, but drugs is the default solution.