It has happened before.
Even I was shocked how tens of thousands of companies handed over mind blowingly valuable customer data to Facebook. They aggressively promoted their Facebook Page to their customer base: please like us on Facebook!
What did Facebook do? They took that data and sold it to competitors as ad inventory. I never saw a single company owner complain. Companies spent millions of dollars and years of effort building up a customer base, and just handed it right over to Facebook.
To put it in more blunt terms, Facebook stole companies assets through social engineering. I saw friends turn around and build profitable, multi-million dollar businesses through this single data usurpation channel.
Will companies get more savvy about locking down their data? I'm not counting on it.