Mr. Gaff, most average people don't worry about this, period. The security in place in any commercial data center is far more robust than what's on your own local machine and hackers target those, too.
What is anyone going to do with your, or my, or anyone's contacts list that requires any real worry? If people want random e-mail addresses these are so readily available by so many means that worrying about their acquisition is a complete waste of time. You simply can't stop it.
The world has moved away from POP because IMAP and synchronization is incredibly important in today's mobile world. That trend isn't going to reverse.
Never underestimate the difficulty of changing false beliefs by facts.
~ Henry Rosovsky