To do evil, I think you need to deny reality. To enslave people, or to kill people on mass, you need to deny their humanity, they are not really "people".How often do you think that those who many might consider to be immoral, unethical, dishonorable etc. are aware of and acknowledge that about themselves vs. think themselves otherwise or be in denial about it?
Rapist convince themselves that "she wanted it", or "when your are a celebrity they let you do it". or again, they are not really people, they are things here for our amusement.
Big or little evil acts always involve some level of self deception.