Amanda of Pandagon's Vonnegut tribute post reminded me of another reason why he, and the literature of WWII in general, was very important.
what I find interesting about Slaughterhouse Five is that it's an angry protest against the historical revisionism that casts WWII as the "good" war.
This is vital, especially in light of what happened in the 90's with the ridiculously over the top mythologization of the Greatest Generation. It confused me a lot at the time, because all of the literature and history of WWII I had read up to then was nothing like that. And most of it wasn't written by professional intellectuals or mythmakers, but by people like Vonnegut and Heller who were working or middle class, and actually fought and saw what it was really like.
None of them seemed to have any illusions that WWII was anything but a senseless bloodbath and a tragedy for humanity in general. Nobody "won" that war. The very fact that it happened to begin with, and that humanity got to a point where things like London, Dresden, Tokyo, Hiroshima, Nagasaki, the Rape of Nanking, and the Holocaust could occur was such an immeasurable tragedy and loss that no amount of heroism and courage could begin to overcome it. Pynchon, who was too young to actually fight in WWII, but who definitely understood it in the same way as Heller and Vonnegut, put it this way:
Yet the continuity, flesh to kindred metals, home to hedgeless sea, has persisted. It is not death that separates these incarnations, but paper: paper specialties, paper routines. The War, the Empire, will expedite such barriers between our lives. The War needs to divide this way, and to subdivide, though its propaganda will always stress unity, alliance, pulling together. The War does not appear to want a folk-consciousness, not even of the sort the Germans have engineered, ein Volk ein Fuhrer - it wants a machine of many separate parts, not oneness, but a complexity... Yet who can presume to say what the War wants, so vast and aloof is it... so absentee. Perhaps the War isn't even an awareness- not a life at all, really. There may only be some cruel, accidental resemblance to life.
He saw the war as some sort of inhuman, irresistable force; machines and systems that we had unconsciously or inadvertently created had broken out of our control. From the literature that came out of it, to the countless grandparents who were not at all eager to even talk about what they had seen and done, let alone cast themselves as heroes, it's clear that many of the people who participated in it and saw the real price on all sides seem to have seen it similarly, and taken the same sorts of lessons from it that Vonnegut and the others who wrote the literature of the war did.
Failing to grasp those lessons is a lot of what got us into the mess that we're currently in. I think the 90's revisionism about WWII was really pernicious, in that it put forth this ideal of a great crusading struggle against evil, with America at its head. That was attractive to lots of people looking for meaning in post-post-everything life. They wanted to be part of a Great Unambiguous Struggle like their parents and grandparents were, to be swaggering heroes like their mythical forebears.
That's a significant piece of how we got from a limited fight against a bunch of dudes in caves in Afghanistan to a full blown Holy War. The only reason people can think it's plausible that Islamic Fundamentalism is an existential threat to our way of life is that they're looking at it through the lens of WWII. They wanted a Nazi Germany of their own to overcome, and, since no such thing existed, it had to be invented. Vonnegut and most of the voices of his generation knew that you should never wish for something like that. After all, they saw what that really meant, and what the true cost was.
This is the only story of mine whose moral I know. I don't think it's a marvelous moral; I simply happen to know what it is: We are what we pretend to be, so we must be careful about what we pretend to be. - KV