It's a chilling effect. Because you probably can't detect who's monitoring you, you must assume all companies do--potentially even the ones that say they don't.

Must the 21st century be characterised by paranoia/vigilance? :(

No, it doesn't have to be that way. But when both corporate government leaders want, and are getting, unparalleled visibility into what we do and what we think; the only practical counter to that is paranoia and vigilance.

There is another alternative - acceptance - something which is much easier on your mind. Acceptance isn't an option for everyone, however.