Many people seem to believe that our wars in Vietnam and Iraq were utter failures that should've been avoided, but there were reasons we went that had bipartisan support. Communism was a pretty big deal back then and it was spreading. And Iraq...would you really be surprised if we did find WMD's? And do you think a guy who gassed his own citizens would possible consider using them on us or our allies?
I'm not sure what the answer is for Vietnam. What I can say is that the US justifiably lost a lot of credibility when it thwarted democratic elections, fabricated an attack on a US warship, tore the countryside apart, bombed neutral neighbors of Vietnam, and despite so many advantages, was utterly unable to defeat a dedicated military force with uninspired US soldiers, and littered Southeast Asia with tons of UXO that still kill people today.
Not that the Communists were much better, the massacres by Communist forces in Vietnam and by the Khmer Rouge and other entities were pretty horrendous, they also contributed to the UXO situation. I suspect much of that would have happened with or without US involvement. Impossible to say, except to note that at a minimum, US involvement didn't stop it.
Maybe we should have just stayed out altogether, and found better ways to contain the spread of Communism
Iraq was a deceitful ****-show from start to finish. The US should not have invaded, period. We should have focused on Afghanistan, on nailing OBL, taking down the Taliban. Total mess, totally mishandled, epic fail.
Bonus question: Would you still say Vietnam was a mistake if we ended up winning in the early 70's?
How? By flattening the entire North with nuclear weapons?
Or, let's put this another way. We successfully invaded Iraq, toppled Hussein, and got the nation to vote. Even if ISIL had not taken advantage of the subsequent weakness, it was still a huge mistake.