Knowing Tolkien was trying to stuff LOTR with references to Christianity, it only makes sense that the human (or human-like) players are frail, and prone to give in to temptation. That's a running theme in Christianity, that people are extremely weak, and need to submit totally to God. I think there is a conflict between absolute good and evil in LOTR, but that good is only hinted at by the protagonists since they are imperfect agents trying to aspire to do the right thing. Same thing could be said of some in GOT, though, as the Starks at the beginning were apparently driven more by a sense of duty and the greater good than anything else. Of course, the agents are weak, and not always very bright, so they often fail.
