I think, what makes the tragedy so compelling, is that most of Michael's steps are understandable to some degree in themselves.
The first thing is, he's acting out of love for his father. He's so filled with it, that he even leaves his beloved Kay alone. He's the only male in the family who cares/dares visiting Vito.
He realizes that he's able to protect his father and that his fearlessness makes him different.
In the two discussions between Sonny, Tom, Tessio and Clemenza, he realizes that his brothers are acting irrationally. And he's shocked by the fact that Clemenza and Tessio "want to kill all those men."
So he takes control of the situation. What he doesnt't realize is that he's making it even worse, especially for himself, which is why I consider him a tragic hero like in the classic Greek stories.