In my mind, the credibility gap that Washington leadership held with its people in regards to the Vietnam War helped to increase opposition to it. On one hand, the administrations of President Johnson and Nixon were placed in an impossible situation. Victory in South East Asia was not going to be seen in the traditional sense of the word. There was not going to be a complete victory of American troops over the Viet Cong because the goal was to contain the spread of Communism. The hope would have been to weaken the enemy at a faster pace than the increase of military and political force in the region. Explaining that to the public was already a complex task. For this reason, it was already challenging to be able to suggest that the administration's promises of victory in the region could be easily understood. Additionally, the number of casualties and setbacks in the American campaign in South East Asia was unforeseen and, when experienced, increased the backlash against the war effort. This reality, coupled with the administration's continual assertion that "things are going well," helped to create a situation where few, if any could accept what was being said as true and what was being done as valid. At the same time, such a reality helped to create a lack of transparency in the office of the White House, and the frustration of this bubbled over in the perception of the Vietnam Conflict.
Someextra points to add to the many above. The Vietnam War was the first truly televised war for Americans. Instead of gathering by the radio and listening to motivating speeches and following the Allied forces' progress (as Americans did during World War II), Americans watched--almost in real time--what was going on in Vietnam. The images of bleeding, burned, mutilated, or dead soldiers were powerful and caused many to question if these losses (which now needed no imagination to consider) were worth whatever the purpose of the war was supposed to be.
Similarly, while the war was still in progress, veterans began speaking out against it publicly. Some told of the constant changes in the war's purpose (at least how it was presented to them) which caused them to question why they were in Vietnam. Others discussed the rules of engagement which differed greatly from other American wars. Instead of focusing on offense and victory, soldiers were told to not fire unless fired upon.
Finally, we have to remember that many of the men sent to Vietnam were baby boomers (the children of World War II vets), and many of their parents raised them in the idyllic setting of the 1950s when Americans wanted to put war behind them and give their children everything that they didn't have. This type of upbringing resulted in a much different type of American young person--not one who saw patriotism as all important or who was willing to go wherever his country called--but one who had already established different goals for himself or herself which didn't involve military service. This is not true, of course, of everyone of that generation (my dad voluntarily signed up and served a tour in Vietnam), but it does reflect the contrast between generations.
In addition to the excellent answer above, I would add:
- the war was an ideological war with no clear goals or enemy. Stopping the spread of communism was the goal, but it was a strategy based on "not losing" rather than "winning"
- the war was limited, but prolonged. The military was not allowed to use its full power. In other words, it was guerrilla warfare meant to contain, not a conventional war based on taking land, or a capital. There was no clear exit strategy.
- the war was unjustified. Johnson drafted the Gulf of Tonkin Resolution before the incident even happened. As such, the U.S. used a "bait and switch" strategy to involve military personnel.
- the war was costly, both in human life and resources. It was war by attrition: kill more of them and spend more than they do.
- we lost. Americans don't support a military that loses, plain and simple.
There were a number of reasons for this:
- Many young Americans simply distrusted any authority and therefore did not trust the government. This got worse as the war went on and it appeared that the government was not always telling the truth.
- Many young Americans believed to some extent in Marxist ideas and did not like the US fighting against communism.
- Many Americans believed that the war was not really necessary. It was not as if the Viet Cong were going to attack us. Some thought this meant the war was pointless. Others thought it showed that we were being imperialistic.
- Many Americans objected to the draft isnce it forced men to go fight whether they wanted to or not.
- It was hard to determine if we were making any progress in the war and so it was hard for people to feel like the war was something that could be won.
- It was not clear that the Vietnamese really wanted us to be there and it was not clear that the government we supported was any good.