evil is the idea that those who oppose you or wish to perform cruel acts have no basis for doing so other than being driven by a mystical, malevolent force
Evil is a philisophical idea, that depends purely on perception of the person, or is determined by society. For example, "evil" in our society, is killing or maiming or torturing.
and that they have no incentive for doing the things theyre doing
and that they are certain to be in complete mental health
Unfortunately, anyone who commits "evil" for your first reason, is
not mentally sound. They typically have "antisocial personality disorder" (also known as being a sociopath) or schizophrenia, or another type of mental illness that deprives them of the concept of morality. Even then, mental illness can cause people to confabulate reasons, such as "god told me to do it", or "I'm ridding the world of the antichrist", and crazy stuff like that.
If they are mentally sound, then they typically have a reason, like Adolf Riddler trying to make the world a better place through the extermination of lesser human beings (this could be considered "evil" in it's own way).
