It made the US government believe in a concept known as the domino theory. The paramount idea in this discourse was that if one Asian nation fell to the leftist ideology of communism, others would quickly follow.
Historically speaking, the year of 1954 had seen the Communist forces in the north of Vietnam, led by Ho Chi Minh, defeat the colonial French rule in Vietnam. Ho Chi Minh chartered a policy whereby Vietnam was divided into a pro-American Southern and a communist northern bloc with a demilitarised zone (DMZ) in the middle. Though, Ho Chi Minh had intended to bring the two sections under one government by a common rule of the ballot, it never really happened. On the contrary, the communist forces began a guerrilla war against the south.
This tempted the US government to launch a battle in Vietnam in order to curtail what it believed to be the rise of Soviet communism. If from the point of view of Utilitarianism, the ethical doctrine that holds that the moral worth of an action is solely determined by its contribution to overall utility, we make an effort to justify the war, we realise that even then the action of the US government was really uncalled for. The US government's stubborn grit to win the war rose to such a level that even the basic tenets of virtue ethics were debunked. In trying to be utilitarian to their cause, the US army indulged in the horrendous crime of using herbicides in order to defoliate large parts of the countryside. These chemicals played havoc, and still continue to do so, in destroying the landscape, causing hereditary diseases, birth defects and poisoning the food chain.
It is estimated that during the years of 1961-1962, the Kennedy administration authorised the use of chemicals to destroy rice crops. Between 1961 and 1967, the U.S. Air Force sprayed 20 million U.S. gallons (76,000 m) of concentrated herbicides over 6 million acres of crops and trees, affecting an estimated 13 percent of South Vietnam's land. In 1997, an article published by the Wall Street Journal reported that up to half a million children were born with dioxin-related deformities, and that the birth defects in southern Vietnam were fourfold those in the north! No amount of utilitarianism can justify this mass killing.
Similarly, the war showed how the entire corpus of reason and Kantian deontology was done away with by the US army operation in Vietnam. As General Maxwell Taylor, one of the principle architects of the war noted
First, we didn't know ourselves. We thought that we were going into another Korean war, but this was a different country. Secondly, we didn't know our South Vietnamese allies .... And we knew less about North Vietnam. Who was Ho Chi Minh Nobody really knew. So, until we know the enemy and know our allies and know ourselves, we'd better keep out of this kind of dirty business. It's very dangerous.
Robert McNamara, Lyndon Johnson's Secretary of Defense, was even more blunt. When asked to comment on his role by the London Observer, he replied "I was wrong! My God, I was wrong!
Thus, the war clearly defeated the utilitarian purposes it stood for. Moreover, the fact that it cost the American government more than $120 billion, apart from vehement protests and scorn the world over, illustrates the fact that the Vietnam War was definitely a grave error