The idea of human rights (as we know today) I would say appeared after WWII and the Holocaust. If Vietnam were fought without T.V. and press, and perhaps 20 years earlier, not only would we have won, we would have probably averted the hippie movement and many other important cultural (or counter-cultural) events. Then again we can only hypothesize... Never know what may happen if you screw with time.
And Yauz what your pointing out is factual but look at it this way:
Germans: High Quality, Expensive troops, better weaponry (overall), each squad lost matters like its your own life.
Allies (cept Brits): Lower Quality, less well trained troops, in many cases more adaptable to environment with numerous upgrade paths, and cheap but mass-producible tanks.
Now flip the script:
Allied Forces in Korea (or 'Nam)-High Quality troops, armed with the latest and the greatest. Can Requisition tons of support, use numerous heavy vehicles,etc. In a Vietnam mod, I can imagine that it would be interesting to implement a system that whenever Allied (or at least American) squads are killed Manpower intake is decreased.
Commies: Cheap easily producible squads with slightly less advanced weapons, can adapt to environment and battle due to familiarity with territory, and better logistics.
Seems to work out quite well in my personal opinion