I remember flipping through the channels a few months ago and seeing a documentary on Michael. They had a psychiatrist speaking of probable psychological reasons as to why he would want to have so much plastic surgery done to him. I believe She said that one of the most likely reasons would be his strong resemblance to his father.
He had many facial features (most notably his nose) that he shared with his father. So it was logical to him that since he carried such a great hate towards his father that having plastic surgery to remove his resemblance to him would be common sense. Getting as far away from any aspect of him he carried, you know?