Hmm. I've long wondered: why do we so often set up "thematic struggles". Does life (which fiction is based on) really have any theme? Every person has their own ideas on what's important. For most people throughout history, it's just been getting through from day to day.
I think a lot of it comes from D&D's alignment system. It forces everybody to stake a position on 2 struggles (good/evil & law/chaos), and makes everything revolve around that. But take, for instance, the knights in Britain & France. Each side thought it was right, both "served God", yet neither was in any objective sense good or evil. They were simply national opponents. The only real theme there is Us vs. Them.
Similarly, humans vs. orcs isn't really about good vs. evil. It's just Us vs. Them.