If we're speaking of "realistic" evil, then neither cliche is accurate. Most people who do evil things to not do them for the sake of wallowing in evilness, nor do they think that they are good people.
For most people, they really don't think about it at all. It's just their job, they're just following orders, or they're just doing what is expected of them, or what is "normal". They pass any responsibility for their actions to the next person down the line, because being responsible for your actions is hard.
Let's take an environmental disaster. The worker who was driving the truck full of chemicals that spilled will say he's a scapegoat, he was over-worked and it isn't his fault. His manager will claim that he's doing the best he can with the budget he has, so of course he has to overwork his drivers. That guy's manager will say that the orders came from above. The CEO will say that he's just cutting costs to please the stockholders, and of course the stockholders have no direct input on the decision that cut the safety funding; they just want their stock to increase in value, and who can blame them for that?
Realistic evil is banal, and generally pretty worthless for heroic storytelling. Sometimes it's okay to just have a matinee villain, when it's well done. Aztechnology is a matinee villain, and Dunk...well, the fact that the closest thing the Sixth World had to a benevolent, Gandalf-esque wise man was a manipulative dragon whose master plan continues to unfold long after his death is how you know we're playing in a dystopia.