I'll put it this way, even McNamara has a book out there saying "we fucked up" in a few thousand more words than that. But does insist that at least the military leaders thought they were acting against a concerted soviet push(domino theory bullshit and all), rather than the nationalist revolutions they were actually dealing with. You know, one of the guys who's absolutely hated for his involvement in the war.
I would in no way be surprised if more political motivations were behind why the war didn't end earlier than it did.