Both Iraq and Viet Nam had deeper and more sinister motives. Let's take a look at these two conflicts and then turn to the underlying motives:
Many apologists say that we "would" or "could" have won the Viet Nam war if we had not been politically fractured as a nation. They point out that we "won every battle." This of course is a ludicrous assertion and at best is irrelevant. We left for a number of reasons not the least of which was the public's weariness of the war.
There are at least two critical differences between this war and the Viet Nam conflict, and one similarity. The similarity lies in the weariness of an endless war with no end in sight and with a steady stream of useless losses of lives.
The first difference has to do with the nature of the warring parties:
The "North" and "South" Vietnamese were not really culturally different at all, and they certainly did not represent a profound philosophic difference in worldview nor religion dating back for centuries. This dichotomy was an artificial creation of the French, from whom we inherited that conflict. If there were any separation it was due to the similarity in culture between China and North Vietnamese, on the one hand, and the created "South" with it's dubious benefactors, on the other.
In contrast, the differences in Iraq are truly sectarian, philosophical and political. The irony here is that this very same Saddam Hussein was the cohesive force that allowed that country to survive as one despite these differences:
Until we arrived on the scene, there was little sectarian violence between Sunni and Shiite during his reign, and this was not just because of Saddam's power per se: Many Sunni and Shiite families lived in peace with one another and even intermarried. The Kurds were not a major threat to either Sunni or Shiite, and they had their hands full, dealing with Turkey, to the north; and the oil flowed.
The second difference has to do with the ostensive reason for and purpose of the war:
Regarding Viet Nam, by 1954 we were supporting 80% of their war effort, so we were committed to a losing situation from the git-go. By 1958, we had inherited a debacle. As one Intel officer told me then, "the people of Viet Nam want to know only two things: Where's my next meal coming from, and who's the boss?" Once inherited, our leaders and their handlers saw benefits to assuming the conflict, none of them rational in nature. (See below.)
The fictitious "Golf of Tonkin Incident" was as imaginary as the so-called "Yellow cake" incident, which together with the arbitrary assertions of the Administration that Saddam had--or was about to have-WMD, frightened a gullible public. A few years before, it had been the allegation that Saddam had infringed on the Kuwaiti oil sources. (Actually it was exactly the opposite: The Kuwaitis were slant-drilling Saddam's oil.)
Because the allegations were proven false by the IAEC, which had inspected Saddam's facilities, we--literally--had no reason for staying. The other assertion--that Saddam had something to do with 9/11 was even more ridiculous, and was proved to be patently a lie.
Let us consider the possible outcome of the current conflict in Iraq, seen against the backdrop of Viet Nam, and in terms of what we haven't learned:
The brilliant planning and propaganda of Ho Chi Minh and General Giap insured the real reason for our demise in Viet Nam:
These men made it clear to the Vietnamese people that they were just that--one people, and that they had to make that simple fact their major focus, that the people would suffer extreme losses and privations, but that this was the only way they would rid themselves of their oppressors. They were right, of course; and incidentally, their brutal honesty was matched only by their moral intransigence and integrity. (There are several books on this subject, but you will not find them in general circulation here.)
In their favor was the nature of the dichotomy between "North" and "South" Viet Nam. The leaders correctly pointed out than there was only one Viet Nam and that the "South" was in large part a contrivance of the US government, which put a weak leader (Ngo Diem) in office, followed by General Thieu and later General Ky, all after the assassination of Diem by the CIA. The fact that Madam Nhu, Diem's widow, together with their daughter, went on TV and emotionally and with disregard for their own safety, told exactly what happened, thus showing this family to be just that--a family, and showed what happens if you trust the US. Anyone who worked for the corrupt "South" government was hated; and all predictions to the effect that the US would abandon him or her in the end were absolutely correct. Even Westmoreland years later admitted that it was a civil war and that the only war of "liberation" was to be liberated from us.