[jammies]

As Hack'n'Lube pointed out quite eloquently, Vietnam was fought in a far different context - as it turned out, it was a mistake from the beginning but at the time there was a certain logic to it in the sense that the US wanted to contain Communist expansion at all costs. Remember this was a world in which African and Asian countries were shaking free of the West, often via revolutionary movements that were only too happy to accept Soviet assistance in doing so, and it looked like the power of Communism was waxing.

In the end, they probably did their cause far more harm than if they'd just let the Vietnamese fight it out themselves, but that was masterful politics by the North Vietnamese and Soviets, who essentially made the war unwinnable by dangling the prospect of escalation if the US had invaded North Vietnam and taken Hanoi - you simply can't defeat an enemy whose base is secure, the best you can do is stalemate. Since the Americans were afraid of what the Soviets and/or Chinese might do if they attacked North Vietnam, they never did so, and despite inflicting horrendous casualties on the order of 10 or 20 to 1 on their enemies, they eventually lost the war because the NVA didn't care how many men it lost and the USA definitely did.

In Iraq, the Bush administration made a different error - they had no qualms about going to Baghdad, but the problem was that Iraq was not the headquarters of the people they were trying to defeat. Sure, Saddam was a thug and a tyrant, but as far as supporting terrorism goes, he was a bit player, if even that. They would have done FAR better to reign in the Israelis, demonstrating control, and then attempted negotiation with the various states in the region to create an anti-terrorist coalition with the implied threat of targeted US action on states that didn't buy in. But that would take diplomatic skill and finesse, which the USA is not liberally supplied with, and not military force, which is a specialty.