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.