In terms of tangible losses, we lost more troops in Vietnam.
Not to mention that it resulted in massive civilian losses on both sides' parts.
In addition, during the war, we also attacked Cambodia, resulting in the deaths of 500,000-1,000,000, and also paving the way for the rise of the Khmer Rouge.
I will agree wholeheartedly with you regarding our horrendous decision in invading Iraq; it was humiliating. However, I do not agree that it was necessary to take on Vietnam. With our without our forces, the South would have most likely fallen. What we did manage to do was prolong the fight, as well as provide the North even greater motivation in their efforts, resulting in a horrendous quagmire, in which both sides were left to wage assault against one another with little ultimate gain. Finally, when the US withdrew, the North hastily proceeded to take over the South, much as they probably would have done if the US had not been involved, though with much greater destruction and loss, as a result of such grizzly warfare over such a long period of time.