I think the potential for evil is in every human heart.I read a book titled. --I cannot forgive. The writer lived in the extermination camps in Germany. I was about 16 when this real life story hit a nerve with my learning about being a human. What I came away with is how easy cruel and evil behaviour can become a normal waking routine. I clearly know that it is not instinctive. It is indoctrinated . Humans will kill and torture other humans if they are trained to do so. Compassion for the wellbeing of others is not a given from birth. It is learned about over time.
Have you ever noticed how very young children act out and get worse if not corrected? If you want someone to be super evil, you start them out at a young age like what happened in Germany before WWII. A buddy of mine did something like that by being pretty rough with his kid whenever the kid messed up. The kid ended up being mean and pissed when he got a little older....I think the potential for evil is in every human heart.