Why didn't McNamara speak out when he could have made a difference?

As an anti-Communist, McNamara may have thought the Vietnam War just. One of the tragedies of McNamara is that he knew at least the means being used during the Vietnam War were wrong and ultimately ineffective. 

There was too much corruption among the anti-Communist Vietnamese and they were out of touch with the majority of Vietnamese to effectively oppose the Communist led coalition. The anti-Communist elites were Roman Catholics (descendants of the converts from the missionaries that as always accompanied the French colonials) while the majority of Vietnamese were Buddhist.

Information such as this was readily available to McNarmara in the Rand Corp.'s analysis, later known as The Pentagon Papers when they were released by Daniel Ellsberg. They were written during McNamara's tenure, classified but circulated within the Pentagon. McNamara was enough of an intellectual to understand their significance. 

Had he spoken out publicly while Sec'y of Defense or immediately after he left office, he might have saved thousands of American and Vietnamese lives. 

Had the war in neighboring Vietnam ended in the 60s before Nixon overthrew the Cambodian monarchy and invaded Cambodia, the Cambodian king might have been able to maintain his relative neutrality, continue to marginalize and isolate the Khmer Rouge. and save Cambodia from the horror of Khmer Rouge rule.

The only way the Vietnam War could have been "won" would have been to attempt to occupy the whole country. The Soviet Union and China were committed to a Communist nation in at least the northern half of Vietnam. Attempting to occupy all of Vietnam would have risked a land war with China which easily could have escalated into a nuclear war with the Soviet Union. Even if we had figured out how to occupy Vietnam without provoking an end of the world nuclear war, we would have found ourselves fighting an insurgency far worse than anything we face in Iraq today.

I'm treading on shaky grounds as the intellectual giants of history urge extreme caution when in speculating on historical "what ifs"!

Had McNamara spoken up when that could have made a real difference, he would have risked losing appointments to various private sector positions and earning obscene amounts of money. Instead he would have had to settle for something as the more modest pay of a job in academia. Was that too much risk and cost to him to do the right thing?

McNamara exhibitted moral cowardice as did Colin Powell. Powell knew the Iraq War was wrong. Prior to the Iraq War, Colin Powell spoke of what he learned from his service in Vietnam about when and how American troops should be sent into combat. He knew that the Bush, Cheney, and Rumsfeld were ignoring those lessons.

Yet while Powell was in a position in power when saying something might of prevented the Iraq War, he told lies to the American people and the U.N. to promote the war.  By failing to speak the truth, Powell betrayed not only his own intellectual and moral integrity but also all of his comrades who served in Vietnam. That makes his silence more tragic.

Powell is no longer being seriously considered for the Republican presidential nomination. His pensions are secure, he is retired and therefore has nothing to risk, Now Powell suddenly discovered his ethical and moral voice. He endorsed Obama  and just made a statement of support for Judge Sotomayor.

Do the comparatively minor risks of some social ostracism. decreased job options, and lower pay cause people such as McNamara and Powell to ignore their moral compasses when their words could make significant difference?