My thoughts are simple. 1) He was a musical phenomenon, truly gifted. 2) He had a life so far removed from normalcy at any stage that he was bound to go "weird", so I don't blame him for it. We see it with 99% of people exposed to this kind of fame - Britney Spears being a recent example of celebs who go off the rails. So I would say that he became unusual as opposed to being born that way.
Tom F