I think you can make a defense for many of Michael's choices, but not the killing of Fredo.
That action made clear that Michael had gone far beyond his justifications of "protecting his Family" or "seeking legitimacy" into a realm of almost inhuman cold-bloodedness.
The real tragedy was that of the innocents (or slightly less guilty) who suffered becuase of Michael's actions.
Yes, but Fredo didn't even feel remorseful in the boat house. Instead, he outlashed at Michael with rage and jealously even though he alsmot had his "little brother killed"
