Good answer, but allow me to expound further...
War: What is it Good For? ...Before you answer that, imagine Europe under decades of Fascist and Nazi rule, the tens of millions of people who would have certainly met a hideous fate, had the Allies not won the war. Imagine the country we may very well live in today, had America never engaged in a Civil War. Or the "United States" being an obscure footnote in British history, had we not fought and won the War of 1812.
So while we can all acknowledge war is bad, and not something we should engage in lightly, it is sometimes necessary and crucial to civilization. The hopeless sentiment regarding Vietnam, is a direct result of us BAILING and not winning the war! If anything, it should have been a lesson to us, not to enter wars we aren't willing to win decisively. But it seems it didn't teach us this at all, because we now have Iraq. The same thing can happen there, we can BAIL and not win, and the sacrifices made will be for absolutely nothing.
Some people obviously WANT that to be the case, so they can politicize the war, and gain power in government as a result. To me, that is appalling and despicable, but it is the mindset of many Americans. What I see in Iraq, is millions of people proudly holding up a purple thumb! Signifying the first time in their lives they have controlled their own fate and had a political voice. Freedom that some of us simply take for granted! WE made that possible for them! OUR boys did that! Millions of people enjoy the same political freedom we enjoy in our own country, as a direct result of the sacrifices we made. It's selfless and heroic, and it fulfills our moral obligations as a civilized and decent people, to have done what we did. I think of how many lives we turned our backs on in Vietnam, how many millions of people died under an oppressive communist regime, because we became too selfish to complete the task we embarked on... then I hear idiots yammer on about Vietnam like it was supposed to have taught us not to get involved!