What is the actual sickness that John has he’s locked up in the asylum but it doesn’t specify.
After some extensive research (googled it) I'm leaning towards Impulse-Control-Disorder. Or IED. failure to resist a temptation, an urge, an impulse, or the inability to not speak on a thought. There's a few forms of it, like sexual urges or internet addiction. I believe John might fit into the aggressive form of it.
I think John was neglected, and then abandoned, by his parents.
He wasn't born with his issues, he developed them.
On TvTropes... I believe he suffers from Borderline Personality Disorder.