While what he did may have been good for the Family, it wasn't good for the family. Michael was too cold, too ruthless. He alienated his brother (OK, not without reason perhaps), he alienated Tom, who adored him, he alienated his wife, and even his children. Although an argument could be made that he had reason not to trust Fredo, Tom was not a wartime consigliere, Kay was not the "good Mafia wife", etc., Michael held them all in such a tight fist that they either had to escape or strangle. As you said, SC, perhaps that doesn't equate to a bad don, but it equates to something that stinks.