Except the units involved in the first exchanges surely defended themselves and once that happened Truman's order to MacArthur not to provoke China and the fact that MacArthur had obviously already provoked them to the point of several bloody border incidents(at minimum), leaving him in effective violation of his superior's orders...
The Chinese weren't too concerned about losses either. In 1953, to make sure the South Korean government understood that they weren't to be making any post-war raids hiding behind US protection the PRC launched an attack on ROK forces that left 75,000 Chinese dead, just to make sure the point was understood.
Right but would you agree that if a lower level commander decided to just act on the situation before him it is possible to encourage action along not only the line but the officers in charge? What is needed is full use of the airforce int he first moments of the Chinese offensive. Long lines of men with little AA? A series of bombing runs may well have ended the offensive and turned it into a defensive Chinese front.