If you doubt my claim, consider two scenes. In the first, Michael, back from hiding in Sicily, finally decides to get married (again) and so tracks down his college girlfriend. Kay, the daughter of Yankee protestants (including a minister), has long known the real nature of the Corleone “family business” but had been willing to overlook it because Michael seemed to reject that life for himself. But after the shooting of Sollozzo and McCluskey, Kay knows that Michael has entered that world forever. (In the film, her realization is implied when she visits the Corleone compound and speaks with Tom; in the book, it’s made explicit when, on the same visit, she speaks with Mama.)