In the early 60s, most Americans were very ignorant about Vietnam. They just saw it as a little concern. They were an extremely confident nation who had never lost a war to date, and whose resources were limitless. So they naturally assumed that all their weapons and firepower would ensure victory in a couple of months. Patriotism was very strong in America at that time. Many people remembered the McCarthy trials of the 1950's, so people were extremely aware of the anti-Communist feelings in the country in the early 1960's.Most Americans believed the 'Domino Theory' during these years, and so...
having to pay higher taxes in order to fund it. Prosperity was in danger, which caused resentment for the war.

In 1971, an opinion poll was done in America on whether the public thought that Vietnam was morally wrong. Sixty percent answered yes, but still forty percent said no. So there was still a large core of the population that believed in the Vietnam War. Therefore, in conclusion, although there was a dramatic shift in opinion, and much opposition to it supported by leading figures in government and pop culture, much of America supported the war effort.