If you examine the issues and opinions of the day, one would draw a different picture of the events leading to American involvement in Vietnam, than if you viewed them from just seeing the results of the war.
Following World War 2, the United States followed a policy of containment regarding Communism. We tried to "contain" Communism to its current areas. However, a number of events worried the United States.
The Korean War of the early 1950s was viewed by us as an attempt by Communist forces to spread their influence. While this was going on, a democratic France was fighting a war in French Indo-China in an attempt to regain their colony lost to the Japanese during World War 2. Even though this involved the issue of colonialism, their opponent was a Communist force under Ho Chi Minh. President Eisenhower sent financial help to the French consistent with our containment strategy.
Eisenhower was replaced by Kennedy who committed ground troops as advisors, and his successor, Lyndon B. Johnson, committed combat troops on a wide basis.
If you believe that Communism was a threat to the United States (which we did back then), and if you believed in the Domino Theory, which said if Vietnam were to fall, so would the rest of Southeast Asia like a row of dominoes, then the American involvement was probably justified.
If you see the issues of the Vietnam War as one between foreign rule over a small country, as Ho Chi Minh did, or sovereignty of your country, then perhaps the US involvement was questionable, at best.
One must also consider that getting involved didn't have to mean sending large numbers of troops to fight the war on the ground. There was the precedent of Korea, a war in which the US fought with somewhat limited objectives and had also limited its commitment in terms of combat troops and resources and appeared to come out with at least a palatable stalemate, and so the idea of a structured intervention was in vogue.
But those two wars were very different, as was the theater of operations. What I think really raises the possibility of the answer that it was very wrong to get involved was the lack of any serious research on the French experience there and learning from their mistakes as we repeated a number of them in our "involvement."
In looking back with the benefit of history to guide, one could easily argue that the U.S. was not in the right with its involvement in Vietnam. Yet, if one is immersed in the time period, things did not appear to be as clear. The United States and its government was clearly driven by the fear of the Communist threat. The domino theory was advanced throughout American thought at the time. This theory stressed that Communism was such a profound threat because if one nation in a region fell to the the Communists, in a matter of time, all of the nations in that region would follow suit. In this light, the Vietnam War was seen as a conflict not merely for Vietnam, but for the other nations in the region. This fear helped to shape and guide policy and action and its pervasive presence almost made Vietnam involvement and escalation a foregone conclusion. This does not excuse the participation in the conflict, but rather seeks to understand it.
In hindsight, it doesn't seem a wise decision. We were a long way from home, in a country and culture we didn't understand, fighting against a nationalist independence drive much stronger than our own motivations.
But was it "right"? Depends in what sense. Was it right to want democracy for another country? Perhaps. Was it possible? Perhaps not. Was it right to drop as much napalm and bombs on what we knew to be civilians? Probably not. Was it worth it? Depends who you ask.
I think the Vietnam War was an unnecessary war, with ridiculous costs. Outside of containment, I can't think of a good reason for us to have fought there.
The Vietnam Conflict changed the way that Americans thought about and viewed war. There were many opposing opinions. For example, there was a lot of controversy regarding conscription in the Vietnam War. Conscription is when citizens are forced to serve in a war by their government. Many men were drafted during this war, many opposing it and many willing to serve their country with questioning it.
Many people also questioned the United States involvement in Vietnam altogether. The United States ended up withdrawing from the war in 1973. Whether or not the United States was right in getting involved in the Vietnam Conflict is really a matter of opinion.
Frequently end justify the means. If we go by this principle, Surely the Vietnam war did not do any good to the USA, the Vietnam, or to any other country in the world. Thus judging with the hindsight knowing the ultimate consequences of the Vietnam war it is not possible to justify the US conduct. I am not saying that it was wrong for the US to get involved at all. But the way US actually acted, was definitely not the right way of doing it.