Imagine this: in an effort to protect the safety of teenagers from bullying and violence, video cameras are installed in a high school gym's locker rooms and showers. Of course, the school principal and police promise that the security videos would never be watched except after an incident is reported.
If you were a parent, would this be alright with you? Why not?
After all, if your child isn't doing anything wrong, she has nothing to hide, right?
If you are uncomfortable with the idea of cameras in the showers, here might be the reason...
The invasion of privacy is in the act of surveillance, regardless of whether the information is ever used against you.
This is what we call Untargeted Peeping. One's behavior in a private environment changes because someone from The State might be watching. Even if you are doing nothing illegal, you don't want your personal habits, routines, or choices to be seen or judged by others. You don't want to be embarrassed or blackmailed.
If your behavior changes out of fear of exposure, then you've lost some freedom.
That's why the camera in the shower is an invasion of privacy, even if the videos are never watched.
It is also why State monitoring of our online activities and communications is an invasion of privacy, even if the data is never formally examined.
Addendum: After I thought up this scenario of cameras in gym locker rooms, I discovered that it actually happened, in a middle school no less!