Michael had free choice at every turn, and he freely chose the Mob life, with disastrous results:
--He was right to think Sollozzo would try to kill his father after the failed hospital attempt. He was wrong to believe that only he could save his father, by killing Sollozzo and McCluskey. Ironically, an idea that Michael himself had suggested could have been modified to solve the problem bloodlessly. The Corleones could have fed the newspapermen on their payroll the story about McCluskey being a dishonest cop mixed up in drugs and murder before, not after, the trigger was pulled. McCluskey was on the take all his life, and the Corleones had all the details because they paid him. The newspapers would have given that story such headlines that the Police Commissioner would have been shamed into providing Vito with an army to protect him, to save further embarrassment. McCluskey and Sollozzo would have been neutralized without any bloodshed. At minimum, McCluskey would have been transferred or suspended pending investigation; with pressure from the Corleone judges, he’d have been indicted for taking bribes. Sollozzo would have been arrested and probably deported as an undesirable alien. With McCluskey alive, the cops would have had no reason to crack down on all Mob activities. There would have been no Five Families War of 1946, leaving it a contest between the Corleones and the Tattaglias—and as we know, Tattaglia was a pimp, alone he could never have outfought Santino. Michael could have married Kay and gone back to college (and we would have had no Godfather Trilogy!).
Instead, Michael chose to kill Sollozzo and McCluskey, setting in motion his abandonment of Kay, his Sicilian exile, the Five Families War, Carlo’s betrayal, Sonny’s murder, Apollonia’s murder.
There are plenty of other examples, too.