I, for one, don't really think it matters if Vietnam soldiers WERE committing war crimes, because I don't think the Geneva Conventions should take precedence over US sovereignty. I admit I don't know too much about the details here -- whether free fire zones really are "illegal" under international law, etc. -- but I don't care, either, except out of pure curiosity.
It matters. First, an "order" to commit a war crime is not a lawful order. Soldiers, sailors, and marines are obligated not to obey orders which are not lawful. Second, when the US assents to a treaty under the Constitutionally lawful prescription, this treaty becomes part of US law. Without that guarantee we could not make treaties in our own interest. The US, BTW, does not subscribe to the most recent Geneva convention, because signing it and ratifying it are not in our interest. (It gives, among other things, elevated rights to terrorists above lawful combatants.)
The US, rightly, has not ratified the International Court. The treaty empowering this denies the rights of accused guaranteed by the Bill of Rights, for example. But it would be in our interests to honor, and for our soldiers to honor, a treaty--if it could ever be made--that guaranteed the Bill of Rights to all the people on earth.
Third, it matters because (as is the case in Iraq today) US soldiers for the most part were given complex protocols to protect innocent lives in Vietnam. To say that it was war and therefore OK denies a tremendous sacrifice made "just" to be on the side of the right and the just that Americans made in Vietnam. Even Daniel Elsberg, of Pentagon papers fame--and certainly no conservative, admitted that atrocities in Vietnam were not common.
"When you slay monsters, you must not become a monster. When you stare into the abyss, the abyss stares back into you."
It is always important to be on the side of liberty, truth, and justice. The claim by VVAW, multiculturalists, communists, fellow travelers, and all their ilk rankles most because if you examine American History objectively, we have taken great pains and made great sacrifices to do what is Good. Even failing, as we often have, we failed through weakness, and not through intention, certainly not through malice. We lost guys in the 'Nam because they would not shoot a kid during the day who donned his black pajamas for ambush at night.
It matters. It is why the SBVT's are outraged.