Why would anyone think otherwise? The Iraqis did not surrender despite facing an overwhelming force and heavy loss of life as Washington spin doctors had told us, did they?
There is little historical evidence that when when hostilities arrupt, the participants loose their will to fight. The opposite is the norm - nations keep fighting despite heavy casualties and defeats. The WW II provides plenty of good examples - Russians fought despite numerous defeats and losses, Germans continue to fight even though it was painfluly obvious that they were loosing the war big time. Ditto for Vietnamese.
Thinking otherwise suggest a gross misjudgment of human psychology which in this case is based on a rather simple principle flight or fight. The "flight" reaction is most likely when people fear something that has not yet actualized, because "flight" is in a way, the preservation of the status quo, whereas "fight" would be changing that status quo for something with an unknown outcome. Most people prefer an unfavorable status quo to an unknown change, especially when change contains cosiderable risk. However, this changes quite radically when the "fight" actually breaks up. There is no fear of the unknown anymore, the fight is the reality and the new status quo, so people will dig in their heels and keep fighting despite their losses.
US is in a peculiar situation, because it has never been attacked by anyone, but instead it sent its mercenaries to attack other countries. So for most US-ers fight-or-flight is seldom an option, because they have little chance of being directly involved in hostilities - so they have little personalstakes in either supporting or opposing a war that their government is waging elsewhere. In most cases, their support or oppostion is akin to rooting for their favorite sports team - they are "for" if the political party they identify with wages the war and "against" if their party opposes it. Since both major political parties in the US support the war, so do most US-esers.
The situation changes when they face a real possiblity to be directly involved in hostilities, as it was the case of Vietnam war. Those who are about to be drafted (and their families) obviously fear being directly involved, but their reaction depends on whether they swallow raw the government propaganda - which invariably portrays every military adventure as 'defense of the homeland' - or are in a position to question and reject these claims. Those US-eser who swallow act as any other group of people who feels that are under an ongoing attack - they fight back. Those who spit out the government propaganda do not feel any need to defend themselves, but instead act as any other group of people who faces but is not yet involved in hostilities and chooses the "flight" reaction.
This explains why many US-ers opposed the war in Vietnam, but are unlikley to oppose a war in Iraq (regardless of its cost)- unless they will face the possibility of being drafted. But before that happens, cheerleading a war carries no personal cost, and has a mild benefit of vicarious feeling good about oneself by joining the majority and, most likely, the winning team. Heckling, on the other hand, carries nontrivial personal cost of being ostracized, but its benefits are no greater than those of cheerleading. So most people opt for cheerleading.
Wojtek