All good points, but I think we are mixing apples and oranges. We're talking about Vito's intentions and Michael's intentions; about destiny which I don't buy because it's 20/20 hindsight; about people's expectations (like Clemenza).

The novel and film portrayal (especially in the Epic) make it clear that Michael had no intention of joining the family business. I don't know how anyone can miss that. That estrangement from his father was mitigated by Vito's near assassination; from then on Michael was with his father as a son, not as a Mafioso. As the novel states, it was in Sicily when Michael began to change when he saw what could have been Vito's life if he had simply accepted his fate. That contributed to his evolution into a Mafioso as did Appolonia's murder. When he returns to the US and sees Kay, he rationalizes his father's world by telling Kay that Vito is no different from any powerful man.