Privacy: The issue isn't (just) other people knowing your information
ALA's Intellectual Freedom Round Table has a blog post suggesting that thinking about online privacy on the 'human scale' (eg, other people seeing our information) is too limited.
So by thinking about privacy violations on a human scale, we convince ourselves that even though the capability exists to track us, our privacy is only potentially violated. For our privacy to actually be violated, someone (Google, Facebook, or the FBI) would have to specifically notice us.
Instead, unexpected correlations like the Star Trek/pedophilia connection may turn innocuous online activity into something that triggers a red flag.