I can understand MJ wanting to go through skin bleaching treatments to hide is skin discoloration (I know it can be bad looking, there was a hispanic from PJP who had similar splotching on his face, you could tell he was uncomfortable with himself as he always wore a beard to try and hide it and always wore a beard guard, but the splotch took up half his face and nearly half his head. I noticed because he had his back turned towards me and I noticed one ear was brown and another was pink. Then he turned around and he had shaven his beard off and half his face was pink and the other half was brown, he gave me a shy smile. I thought he had burned himself badly and the skin had just healed back pink and the pink coloration was scar tissue, but then another guy told me that he had a skin disorder.
But then MJ went under the nose jobs because he was unhappy with his appearence, he starved himself down because he didn't want to be fat. After an abusive childhood, and having grown up in the spotlight to look perfect every moment your out. By the time he set out on his own, he was broken. He felt a huge chunk of his life missing after realizing he didn't have a normal childhood. This is why he was obsessed with Neverland and Peter Pan, in Neverland, you never grow up. In his mind, when he was at Neverland he could be a boy again and tried to capture pieces of his childhood he felt that he missed out on.