I think many many people have understood the depth of Facebook's tracking for a long time now. The issue is that most people didn't care as long as it was all for the sake of ads and revenue. It turns out tracking can be much more sinister than that. Manipulation of elections is just the tip of the iceberg. When you know what activities/relationships impact a person you can make a psychological impact. The issue at hand is all about epistemology; Facebook can alter/pretend to be a source of authority based on beliefs you have expressed or people you follow. This is what happens when people are willing to abandon innate freedoms for convenience.
You're right, people generally know their information is being downloaded, they just don't realize what it can be used for and they don't have a choice. These big companies have almost monopoly power so you either agree to let them use your data or you can't use their product. And they all collude so there is nowhere to go for the consumer. I'm normally not a big fan of government intervention but it seems like there needs to be an update on the Sherman Anti-Trust Act and other such trust busting laws.
Problem is, there are many powerful players in the field. Another problem is, I'd rather talk to people on the virtual street without feeling like I'm being watched. I haven't lived through the Soviet Union, and I damn well would rather not.