How we cite our quotes: All quotations are from The Godfather.
Quote #4
TESSIO: Tell Mike it was only business. I always liked him.
Michael observes that Tessio turned traitor because it seemed like the smart thing to do. He doesn't really blame him for it, and Tessio doesn't really blame Michael for killing him. From both of their perspectives, it really is "just business."
Quote #5
CONNIE: Why do you think he kept Carlo at the mall? All the time he knew he was going to kill him. And then he stood Godfather to our baby. You think you know your husband? You know how many men he had killed! Read the papers. Read the papers! That's your husband!
Of course, Connie's husband also helped murder her own brother, in addition to beating her. So, Michael, by his code anyway, needed to kill him. (There might be better reasons for thinking Michael is a monster than this one, though.)