Not only were the initial reasons for joining the War justified (The Gulf of Tonkin incident) justified, but the United States had an obligation to defend South-Vietnam and American-interests. First, many like to claim that the initial attack at the Gulf of Tonkin was a fake, but then August 2, 1964, the destroyer USS-Maddox was attacked by North-Vietnamese boats, the August 4th attack was the false one that people so often point out. Another reason for our involvement was to protect American interests; however, when I say American interests, I don't mean money, like so many on the other side like to propose. This interest, however, was that of liberty-and the waging war against the communists. The United-States had stakes in defending South-Vietnam well before the Tonkin incident; we were there to protect the South from the Communist. Kennedy specifically was warned of the Communist threat in Asia by Eisenhower and Kenney would later state that America would "pay any price, bear any-burden, meet any hardship, support any friend, oppose any foe, to assure the survival and success of liberty." It was not upholding this promise in 1975 when we left Vietnam, which led millions of South-Vietnamese to their deaths through Communist dictatorship. By early-1970s, the war was almost over, and the North-Veitmanees had started to discuss ending the conflict, but conflict in the US over ending the war quickly and leaving Veitnman would eventually bolster the North-Veitmanees to keep fighting and wait out, which worked out in their favor. The US-left a conflict that was won, and the South Vietnamese, 60,000 Americans, and South Asia suffered. Unless you believe that Veitnman being communist was a good thing, then you should support US involvement.
I also noticed that some opposers claim that US involvement has historically lead to greater civil conflict within the country. The middle-east being the preferred example, and I full-heartedly agree with this example, but not for what you think. The reason for US involvement in the middle east has done more harm than good that again we left an already won conflict. The war in Iraq was won, but we ended up leaving in 2011, allowing other terror-groups and other countries to get involved and pester further conflict. When the United-States ends a conflict and stays to finish what was started, what turns out is better than when the conflict began with, Germany and Japan are good examples. The United States stayed after the conflict to fix what was broken and ended up creating strong allies and some of the freest countries in the world. Japan simply doesn't go from what it was in WWII (an oppressive nation with no concept of freedom) to one of the freest-counties in the world within half a century. That doesn't just happen, and it was thanks to America that the people of Japan and Germany have it so good today.
In conclusion, American-involvement in the Vietnam War was justified, in preserving freedom, defending America, and Asia from the Communist-disease.
The american side lost 60,000 men whereas the northern side lost two million and the more they died in the north the more the american side won and in a war of attrition the Americans would win.The only real way we would lose if some idiot demarcates decided to stop giving the south supplies when we pulled out and lied to the south because of inconsequential backlash.
The U.S. was justified in our involvement over there. The South Vietnamese did not want to be apart of the north except for the Viet Cong. It was a war that we could have easily won of we had kept the pressure on the North and not caved due to protests. We had brought the North to peace talks but when Nixon out we pulled out and the South was not able to protect them self from the North and they were conquered.
The main reasons for our involvement were an attack against a U.S. ship which was later revealed to be fake, made up by the standing President.
The other reason was the "Domino Theory" which was also proven to be false after we lost the Vietnam War and no other countries flipped to Communism.
The U.S. should never have sent soldiers to Vietnam. We were acting in our own interests, not Vietnam's. After winning World War 2 and the Korean War, we began to see ourselves as invincible. Every administration from Truman to Nixon knew that their expectations were not being met, yet they continued to send soldiers to Vietnam to avoid the humiliation of admiting defeat.
The US is always trying meddle in international affairs and here is a perfect example of it going wrong, a waste of resources and so many lives lost. Always acting as the protector of democracy. In reality t was all just a sham in order to protect American interests. Just like what is happening in Syria helping rebels against the government just for a stronger presence in the Middle East