The device that makes Vito seem sympathetic is repeated in II with Fredo. Even though Fredo betrayed his brother simply because he was "passed over" and more likely than not did know
it was going to be a hit on Michael, at the end we feel saddened that Fredo was killed, and we dislike Michael for taking vengence.
There is a big difference. fredo was never a killer. He certainly didn't want anything to happen to his brother. Vito was not a violent mobster but he still would use violence to get wahat he wanted. Mike just became a psycho when he became don
