Well, according to Hulk Hogan's book and this website...
http://www.wrestleview.com/info/faq/hogan.shtml
It was Hogan's idea to turn heel. Now some of you may think that the info I have is not enough proof but where is your info that claims it wasn't Hogan's idea?
I agree that at Wrestlemania 9 was wrong and Hogan should not have done that but clearly McMahon didn't care. And all that matter was that the fans went home happy and I have seen the main event match at Wrestlemania 9...I saw it last week infact on WWE.com on it's WWE 24/7 service. And the fans were very happy when Hogan won.