Jonah Goldberg has written an excellent essay about how we see America's current war through these two particular historical lenses:
Nonetheless, there are two problems with all this historical cherry-picking. The first is our own collective ignorance about history. As a culture, we have a tendency to look for our car keys where the light is good. Our usable past is the past that is illuminated to us. One of the main reasons we leap to analogies about World War II and the Cold War is that it’s the only history most of us know. It’s telling that military histories about World War II (the “good war”) vastly outnumber all others. People don’t call the History Channel the Hitler network for nothing. Meanwhile, Vietnam (the “bad war”) feels like only yesterday to baby boomer liberals, so they have a tendency to see LBJ, Nixon, Robert McNamara, or other ghosts of “quagmires” past haunting the Bush White House.
But surely the ocean of human historical experience cannot be summed up in terms of the tributaries of Vietnam and Nazi Germany.