Just my opinion,but I have always felt that in the early stages of Mike's involvement,he really believed that what he was doing was necessary to protect his loved ones. But as time went on,he began to like it. As he became more powerful,the sickness inside him began to show itself.
In my view,it was there the whole time. Michael became a modern day embodiment of one of the decadent Roman Emperors,a man with absolute power over life and death,a man who had a paranoid streak,and a man with delusions that told him,as Hagen said ,that he had to wipe everybody out.