Mike did not expose the family to the horrors of the world. Vito did the moment he killed the Don in Sicily, at that point he and his family became part of a criminal element. Mike did not join the mafia he was born into it. His choice to kill Sol and the Captain was a decision he made to protect his family, he knew it had to be done, he did not turn evil, in his mind killing Sol and the Captain was no differnt than killing Nazi's both times he was protecting his family. Mike would have been evil if he killed indesciminetly, but he didnt, ever person that he had killed were killed to protect the family, which is what he believed his job to be as the family head. I think that what everyone is seeing as hard is in actuallity the result of a person being thrust into a world and life he never really wanted to be a part of but had too with the shooting of Vito and the death of Sonny. His continual efforts to take the family legit is in my mind a sign of remorse and desire to leave a world he never wanted to be a part of. Sonny wanted that life and taking the family legit would have been the last thing he would ever want to do. In my opinion.