Welcome, Sinister--hope to see many more thoughtful posts from you!
I believe that Michael had choices at every stage of his criminal career. He could have chosen not to commit any of the crimes he was involved in--starting with the murders of Sollozzo and McCluskey. But, as Vito said in the novel, "A man has but one destiny." Any of us might commit crimes if we were exposed to the opportunities. Most of us won't, or don't. But Michael chose the life he led--he wasn't forced into it. This isn't to say that there was no element of tragedy in his life, or goodness, but his choices made his life.