What are the chances of dealing with a real life Michael Myers type (1978 original) like this:
In the original version, Michael doesn't come from an abusive household. He has both parents, an older sister that's concerned about his weird tendencies and a baby sister. When he's only 6, he goes crazy and kills his sister.
According to the further description his parents were worried about him, would visit him on the medical facility and were hoping there was a cure for their son but they died in a car accident.
Another example would be the movie The Good Son... he was evil even with a good upbringing.