There’s obviously alternative explanations about immoral behaviour. How about an example like Charles Whitman?
Killed his mother. Killed his wife. Climbed a tower and shot and killed another 14 people randomly. Pretty evil right? The power of the devil? Maybe.
Whitman also left notes in a diary talking about the irrational, out of character, violent thoughts he’d been having, along with persistent headaches, and requested doctors perform an autopsy to establish if there was a biological reason for his intrusive thoughts and actions.
After his killing spree, and he’d been killed by cops, doctors found a tumour, pressing on his amygdala, an area of the brain associated with emotion and behavioural control.
Evil guy? Morally corrupt? Possessed by the devil and evil spirits? Or just terrible bad luck to have a tumour in just the wrong place of the brain.
It’s easy to imagine that violent and psychopathic behaviours are ultimately resultant of some sort of physical, biological fact about the brain, not a tumour necessarily, but some physical defect or abnormality.
Not sure an unprovable, devil hypothesis helps to explain a great deal here.