I just don’t believe that bad people know they are bad. This notion makes me think I’ll be able to construct compelling villains. I also makes me think that it will be harder to do so. How does an author compel good people to do evil things?
If you think you are in the right, then your actions won’t be evil in that sort of innocence way. Me stepping on a bug isn’t great for the bug, but I don’t spend much time thinking about it and neither do those around me that see it happen–survivor bugs excluded. So for me that’s not evil. At these extreme, evil become solidly tied to the perspective of the actor. That in turn erodes the concept that some event or action can actually be inherently evil.
So now the doer of evil has to be aware of the results of his actions. Which makes the challenge of having bad people that don’t think they are bad more challenging. Maybe you alter the perception of the bad guy. The audience and maybe the good guys don’t perceive a large enough gap between the bad guy and themselves to fall into the bug extreme, but the bad guy does. So bad guy sees bugs; good guys see other guys that ought to be good.
That path lends itself to a caste system or to just outright discrimination.
Another version of that might allow me to have bad guys that just don’t care about what happens to strangers. It’s OK for me to squish bugs and humans alike when I don’t know either one of them and my actions either won’t be found out or they won’t be judged harshly by my peers.
That’s how I get to dictators and leaders of groups and countries. If you are surrounded by fellows that don’t believe or can’t know what your actions are doing to others then you bad guy is golden.