in Vietnam but without the press being on hand to document every event.
This is not just an American issue, every nation has done the same thing, you can't train people to be killers of other people strictly by a rulebook, it doesn't work that way, once you have crossed the taboo of killing another human being anything is possible.

Look at pol pot in Cambodia, the Japanese in WW2,slightly further back in history, the dark ages brought terror to most of Europe.
My own country invented the concentration camp which killed hundreds of Boar women and children, these acts if inhumanity will be with us for as long as we walk the planet.