One of the tragedies of the war was the physical effects of the widely used defoliate Agent Orange. When in long-term contact with humans, it creates all kinds of neurological disorders. One of my best friends has facial tics from Agent Orange exposure. Why did the US govt deny the harmful effects of this chemical on its troops for so long?
On one level, government denial in the harmful effects of Agent Orange resided in plausible deniability. The government commissioned study after study and there was no asserted link between the use of Agent Orange and harmful effects on people. The government's denial was rooted in the idea that Agent Orange was used as a defoliant, something to assist in the efforts of US troops that were fighting. It would be counter- intuitive to suggest that the use of the agent was hurting US troops when it was sought to make their experience "easier."
Another reason for denial might rest in litigious action. If it could be proven that government use of Agent Orange was harmful to troops, much in way of legal action for damages and health costs associated to its dispersing could be sought. The government denied, in a sense, to escape legal ramifications from its use and the effect it had on the soldiers. In this light, denial can be seen as another way for the government to distance itself from the soldier experience in Vietnam. When soldiers returned home, their reception was an awkward one. People did not know what to make of their experience as it was, for the first time on record, a "losing" endeavor. The distance that Vietnam Veterans experienced was echoed in government's distancing from these veterans. As seen with denials in the use of Agent Orange, American society and government had a difficult time in acknowledging the experience of the soldier who served in Vietnam.