If you watch Michael watching Sonny(and Tom) in action... to me he is observing a man... acting as Don as a "rudderless ship"(someone else's descriptor of Sonny's donship on this board)
I think Michael became VERY "concerned" when he tells Sonny "he's my father too, I want to stay" at the Tom and Sonny meeting.
Michael had just gotten in from hearing his father had been shot, so he was concerned over his father and over what his brother was planning to do. True, he disapproved of Santino's "hit list," saying that's not the way Pop would play it, etc. But, in times like that, times of great stress, its hard to know the right answer. Santino was enraged that his father would be hit; Michael's reaction was slow and steady wins the race. Michael thought Santino was wrong, but was he really? We all know that Michael himself was not a good Don (lacking humility and heart), so what makes Michael a judge over Santino?
