Let me argue by analogy.
Changing diapers is an utterly necessary part of parenthood. That doesn't make 'em smell like rosebushes. If you don't, however, the whole house ends up smelling like crap, the kid gets a henious rash on his butt, and the environment is created for a lot of crazy parasitic infections and/or diseases. That doesn't mean changing diapers is the end-all and be-all of parenthood, however.
If you want kids (or end up with them in spite of your wishes), you deal with diapers. If you want to live on Planet Earth with a couple billion greedy assholes, you deal with the reality of violence.
2) As a further development of this point, war creates nothing good. Nothing positive comes from killing folks. Stuff gets blown up, people get hurt and die, and that's as much a definition of 'war' as exchanging carbon dioxide for oxygen is a definition of breathing.
What war does is prevent people from either stealing or destroying things of value that your society has. It creates nothing good, but secures the liberty to create everything of value.
3) Korea was not a loss. It was our most misunderstood war.
Korea was not a declared war because of the new understanding of war created by the idealistic bullshit spun around WWI. Back in 1898 we fought a couple wars like Korea, but backwards. We didn't like what someone was doing with their colonial empire, so we took part of it away. Korea was a case of an imperial power (Soviet Union) using a proxy state to try to take away one of our proxy states. The great game of states, as it has been played for millenia. We stopped them cold, then tried to take away the Soviet Union's proxy state. Another imperial power decided they liked having DPRK as a buffer zone against our proxy state, and committed troops to restore the situation. So all parties settled for status quo ante bellum, more or less.
Here's where the disconnect is. Americans don't like/understand wars fought for reasons of policy. WWI was supposed to be the war to end all wars, instituting an era of international peace and brotherhood where we would all be reasonable and sing kumbaya while holding hands around the damned campfire. Because to tell the truth--that the United States was fighting to preserve French and British colonial empires from a competitor that was not substantially different in any way, in a war that the French and Russians provoked deliberately with British cheerleading--would not have played in Peoria.
So 20 years later, when the Germans finally decide that the irrational and punitive "peace" conditions are not something they are interested in tolerating any longer and restart the war, FDR and Winnie Churchill, in order to bring a reluctant US population in to preserve the British Empire AGAIN, sell WWII as a great moral crusade. After the war it turns out that sure enough the Germans and Japanese were genocidal lunatics this time around. Hooray, the "moral crusade" propaganda and the reality actually line up. It's shocking, I know. First time in history since the baby-sacrificing Carthaginians went out of business.
Along comes Korea. Classic limited war for limited goals, not a grand crusade against evil to crush it once and for all, blahblahblah.
But America doesn't want to hear that. They don't want to hear that it has more to do with power politics as they are played in the Real World than grand ideas. So Truman soft-pedals the war. This scheme is taken to an even more irrational extreme in Vietnam, which is why the American public did finally abandon that war when we were not losing by any rational definition of the word.
4) The above is not intended as a slam on the actual goals of American foreign policy. On a whole, they are far more decent than they are given credit for--and if decency is good business then it is good business. American foreign policy is driven by the fact that people who aren't killing each other make far better customers for McDonalds and Hollywood movies than people who are worried about the savage the next bush over knocking them in the head with a machete. Might be a selfish motivation, but the end result is that we keep trying to keep savages from knocking each other in the head with machetes. Contrast with European colonial empires which tended to pick one particular group of savages, make sure they had all the machetes, and put them in charge of knocking the other groups of savages over the head if they didn't behave.
This is why Iraq's small Sunni minority has run the damn place for decades. They were the British's favorite savages.