On the topic of having nothing to hide, the following description of how 'privacy' differs from 'secrecy' really opened my eyes to the importance of the whole privacy issue and why not having anything to hide isn't an excuse to give up your right to privacy: What you do in the bathroom is not a secret, but you still want to close the door—you still want your privacy.
Everyone knows what happens in the bathroom, but everyone also understands that you have a right to your privacy in there and they don't expect you to leave the door open (unless, of course, that's your thing).