One evil is to treat another person as a thing.
A more subtle evil is to think you know what's best for people more than they know themselves. Among other things, this allows you to justify the ends.
You could also read up on Dante's
Divine Comedy for some classical ideas as to what "evil" is. See
this translation by John Ciardi, or an updated version of
Inferno by Pournelle and Niven. That last is out of print, but used copies are available. No, I'm not interested in selling mine.
Think of it as research.