From the murdering of his pet rats and of cats, Michael Myers showed common signs of one who would grow up without a conscience. Him not feeling bad about killing animals or his family suggest that he most likely would have Anti-Social Personality Disorder.
Michael also spens most of his time making masks, masks he uses to hide his face. He does this so that he can hide himself because he believes that he is ugly. The masks make him look cooler, as well as hiding his face. This is evidence of body dysmorphic disorder.
As clearly shown, the psychological aspects of this movie are very real and are possible. Does this mean we are saying that Michael Myers could be real? Well there is still the aspect that he was shot several times and he still comes out alive.
If there were a slasher out there like Myers, he would easily be put down by the law force.
The original Michael Myers mask