I don't think evil is a helpful word - it's way too loaded.
Firstly it has religious overtones, ideas of sin and forces outside of humanity.
Even taking out the religious element it has images of irredeemabily - the idea of someone being "evil" that they can have no good side.
People like to use it in vilification attempts of someone - so many people don't like complexity and can't cope unless they have bad guys in black hats and good guys in white hats.
You're seeing this right now with Gadaffi - Yes the man was a ruthless dictator who wold torture and kill anyone who opposed him.
He also spent a lot of money in healthcare in his country and built a canal to bring water in land in Mali
He founded a foundation that worked with poverty, drug abuse and mine clearance
http://en.wikipedia.o..._Charity_Associations
But people don't like complex characters - they want to call them "Good" or "Evil".
In the end it's just a label that expresses nothing more than a mob disapproval