The Barkeep idea is perfect. An ordinary person who is really dedicated to seeing evil for its own sake can do a great deal of damage by spreading lies, or just distorting the truth. They can be the motivation for a great deal of evil, but never draw enough attention to themselves to be noticed by adventurers or other potential agents of good. In game terms such a person would have to be LE or NE to keep from drawing attention to himself.
I can picture some little village full of angry rude people. No one is happy and the crime rate is high. Out of this enviroment seem to come several noteworthy villans, a mortician who has turned to necromacny, a particularly violent criminal gang, etc. And no one ever knows its just the local barkeep, or barber, or deputy sheriff who keeps it all going.