People are using the excuse "The US just left, retreated or pulled out" too much. They want to keep the United States's perfect war record.
Despite the Vietnam War never actually being a war, even if it is just a police action, it would be consider a failure.
The reason why the United States went into Vietnam was to help South Vietnam defend against the communist North Vietnam. Well, Vietnam today is communist so that should be the easiest way to say that the United States had fell.
Another excuse is that "The United States only pulled out because they know that fighting was pointless and victory is impossible." Well, that's just an excuse. If you are unprepared to fight a war, you don't deserve a victory. The United States should know the challenges they face going to a battle, even if it takes forever. All the economic and political challenges, for example, what would the war have affect on the economy? The United States leaving because the war is too expensive is not an excuse. If the United States is unable to fund it's soldiers or afford the weapons, it's their own fault for being so unprepared or inexperience or even to generate money. The North Vietnamese were determined to win, despite having heavy casualties.
Another excuse was that the United States killed more people so they won.
Okay, so since when casualties is the main focus in a battle? There are bigger focuses too like objectives. Obtaining land is one of the key objectives in World War II. Despite killing more people, what good was that? If you killed so much people, how come you weren't winning? Remember, the United States had better technology.
Pulling out is a loose term for admitting defeat