Exactly. That's why I think that many Board members have it wrong when they cite Michael's "I'm with you now" statement to Vito when he was in the hospital. That statement represented Michael's renouncing his estrangement from his father (such estrangement is explained in the novel and somewhat also in one of the Saga's scenes). It was not meant by Michael to represent his commitment to his father's crime family and its machinations. As you appear to point out, such commitment was, in large part, a function of Appolonia's murder and Fabrizio's betrayal.
I agree with your analysis, Oli. I don't think Michael could have envisioned himself as being an integral part of the family enterprise when he said, "I'm with you now, Pop." And in any event, Sonny was still in charge. Even his decision to whack Sol and Mac was made to protect his father against another attempt on his life (and perhaps in revenge for Mac breaking his jaw, but let's not go there now).
By the time of Appolonia's murder, Michael was no longer a "civilian" because of his murder of Mac and Sol, and was a hunted man. And, Sonny had been killed. Arguably, his decision to become the Don-in-waiting was taken because there were few if any other options available to him after that point.
I'm not so sure. Michael saw that Sonny was not a good Don when he sat in on the meeting when they brought the dead fish. He planned the break up with Kay, and when he got to the hospital to find no guards there, it confirmed his belief that he was better equiped to take care of Vito than Sonny was. When he tells Vito "I'm with you now" he means it more than metaphorically. I do believe that Michael thought he could be a part of the family business and remain legitimate , a self-delusion that followed him to his death, and I agree the killing of Apollonia cemented his resolve, but after Michael told Vito he was with him, the next things he did were telling. He got Enzo to pretend he was a hit man, he provoked McCluskey, and then he took over the meeting the next day when he literally vetoed Sonny and Tom's plan to "wait."
"Io sono stanco, sono imbigliato, and I wan't everyone here to know, there ain't gonna be no trouble from me..Don Corleone..Cicc' a port!"
