I don't believe any of McNamara's self-serving claims. He did more damage to the Defense Department than any single individual in history with the possible exception of Bradley Manning.
Different perspective of Vietnam from
https://www.peakingat70.com/lets-talk-america/:
From where I stand, the Left has accomplished its goal of making SW Asia another Vietnam with the same kind of treasonous backbiting, mythological storytelling, and outright lying propaganda. There were a lot of good reasons for being very careful about going into either Afghanistan or Iraq and some of our reasons for going into Iraq later turned out to be based on bad intelligence but as Del Vecchio says about Vietnam and soldiers saying we were winning when they left, we were winning in Afghanistan and Iraq before the Democrats took over Congress and before Obama got in the White House.
I don't accept the myths created by Burns or Sheehan (IIRC, Stearman saw that Sheehan was undermining the war effort with slanted reporting from the moment he set foot in Saigon). Vietnam was a tragedy for both the US and the Vietnamese people but it's not made any better by the Left's propaganda.