From my perspective, 'evil' and 'badness' in people are the result of an absence of empathy.

I find that what changes a person's way of treating others the fastest and most permanently, is when that person becomes able to put his or herself in another person's shoes, and know what the other person is experiencing. The exception to this, of course, is sado-masochists. I guess when they cause suffering, they're treating others in the way they would like to be treated themselves.