I have to support Trilogy a bit. I think the movies make a good work in showing Michael motivation for his actions.

I think Michael loved Kay and his kids more than he loved Fredo (he is so stupid that he almost got them killed so he has to go).
He loved Sonny more than he cared for Carlo or Connie's feelings (and he was also a security risk).
He loved his mother more than he wanted to destroy Fredo after what he did to Kay and the kids.
He loved his father more than he could refuse to take over the family. And he started killing to protect him and his siblings who were in immediate danger because of the policeman.
He tried to protect Fredo and Connie and Kay but he wanted to protect them with sheer power (not letting Kay go out for shopping etc).
I think the movie also shows why Michael thinks that power is the only way in life (the betrayal of his father when he tries to play nice, corrupt police, his jaw is broken, the recurring racism he is facing even when he is powerful).He tried to be a soldier to get respect, tried to go to good school but the the society is not really appreciating his efforts to fit in to say the least.
Were his actions forgivable? No and he knows that.
Could he have done differently? If he was not compassionate about his identity, father, mother, wife, kids.. maybe.
Did he completely destroy all of his human relationships while he was trying to protect them? Yes.