Turnbull brings up some good observations and points. However, I disagree with many of them. It's easy to look back now and say whether Michael should have done this or should have done. He did what he thought was best at the time and from we can tell from all the mob movies and even real life mobsters, life in the mafia rarely ends happily. Now to address his 4 points.
Response to First: I don't think the cops would have been shamed into protecting Vito. They would probably rather throw McCluskey out of the police force and label him as a corrupt cop then use their manpower to protect Vito. Furthermore, simply protecting Vito doesn't solve the problem of Sollozzo who would keep on trying to kill Vito. Maybe he would try to bribe another cop into doing it or poisoning Vito through a nurse or numerous plots. As the Godfather book states, all Sollozzo needed to do was take out Vito and the Corleone family would have to go his way. If the Corleone family doesn't try to retaliate against Sollozzo and simply tries to protect Vito, they are made to look foolish and weak. Eventually, Sollozzo would have killed Vito. Also, the Tattaglias and Corleones would have eventually fought if not over the drug issue, then something else. As Clemenza said in the movie, mob wars are inevitable and happen every 10 years or so.
Response to Second: Wow, so you want Fredo to become Don and Michael to go legitimate?? Guess what would have happened? The Corleone Family would have been picked apart and destroyed by its enemies as Fredo is not nearly as smart and ruthless to take control of the family. I'm not even sure Michael would have been safe if he tried to become legitimate. As Vincent said, Michael had to take control to save the Family, which he did at the cost of his own happiness and dreams.
Response to Third: I think many of the events set in motion in the Godfather Part II can be attributed to Fredo and not Michael. Fredo's betrayal allowed for Michael almost become a target of a hit. You see that after the hit is when Michael goes away and tries to find out who the traitor in his family is setting in motion what happens in the rest of the movie. It is my belief that Fredo would have eventually betrayed the Family if he didn't go with Roth as he took sides with Moe Greene in the first movie and Michael said "don't ever side against the Family again" or something like that. Fredo is stupid and wanted power and respect for himself and he would have taken any opportunity to accomplish this. As we see though, he let himself get played by Roth and Oala so he jeopardizes the entire family.
Although it is a tough decision, I think Michael had to order the execution of his brother Fredo although he broke his heart. Fredo has proven to be stupid and his actions almost got Michael killed and the entire Corleone Family ruined. Fredo may have jeopardized the entire family a few years later if Michael didn't do something about it. Again, Michael had to think of saving his family.
Response to Fourth: By this point, although Michael tries to become legit, it is really difficult. He has made too many enemies. He tries to cut ties with the Commission and he is close to doing so but Zasa and Lucchese drag him back. And also, I don't get this last part about Michael gathering his family. So Michael is not supposed to have any family gatherings for the rest of his life because an assassin is after him?? Obviously he trusted Vincent to provide enough security but that didn't work out. I guess I can see your point here though. Perhaps Michael could have gone into hiding until the assassin was killed or everything resolved but then again, who would know if another assassin is sent to try to kill Michael again? Would he really have to hide for the rest of his life?
Although Michael ended up pushing most of his family away, I think he did as best as he could to protect the Corleone Family. He was as Connie said, strong for the Family and sacrificed his own happiness and dreams to keep the Corleone Family in power.
