I think he learned a lot from his mistakes and tried to tell everyone the lessons he learned. Everyone has been too busy to listen. In the end I think he really did understand the extents people would go to.
His lesson from Fog of War that "Rationality will not Save You" and the story he tells of Castro is just drop dead scary.
I guess I should have stated "....during the War..."
There is no question that McNamara fully admitted the mistakes of the War and the things that he had learned. He went on to commit his Life to Nuclear Non-proliferation; non-military aide to poorer countries; and how the mistakes of Vietnam seemed to have not been learned, especially in Iraq.
McNamara's book, In Retrospect and his public pronouncements were rife with self-exculpation.
Remember, even as he prosecuted a war he thought unwinnable after 1965, it was not until 1967 that he had a change of heart, and not until November 1 that he sent a memo to LBJ (alone, no other cabinet members were informed) indicating his doubts and his change in policy. LBJ allowed him a quiet exit, but McNamara did not make a public statement repudiating his own stand. He did not speak against the war, because he feared bringing "aid and comfort to the enemy." (PBS interview, and Robert Dallek Flawed Giant p494ff.) Apparently, he did not give direction even to Clark Clifford.
Is contrition necessary? No, perhaps, but principles are desirable.