Agent Orange used in Vietnam to defoliate was deadly, not only in biologically warring against the agriculture and means of survival, but also by direct impact on the people who ingested it. There is no moral barrier in the U.S military to using toxic or radioactive or any other effective killing means against those we attack. Quite the contrary, the U.S. military searches out such options vigorously, impeded in their use only by the price of dissent or by geopolitical concerns, problems of precedent, etc. Here the situation is marginally more complex, though no more moral. Soldiers are fodder.
Generals don t take up residence on the field of combat, it s too dangerous.
The troops are the expendable ones. If you read the Pentagon Papers reports on Vietnam policy making there is virtually zero concern for the well-being of replaceable troops, per se. There is, however, considerable pragmatic concern about troops morale, about their ability to fight, and about the dissent that can arise in society against war and against the troops lack of safety, as well as about law suits on the troops behalf, for that matter. Though not moral, all this pragmatic concern powerfully militates against the U.S. knowingly using or continuing to use methods or equipment that endanger its own troops unduly. Yes, they could, if the reasons were strong enough.