Why do people overlook tribal warfare?

Somehow people have gotten this romantic, almost Hollywood-style image of the "noble savage" in their heads. The only reason we see the few native people left around the world "living in harmony with nature" is that they either lack the knowledge of metallurgy to make better axes to cut down trees (or people), or they lack access to better crops and cultivation methods. The best book I've ever read that explains why this is a ridiculous myth is Guns, Germs and Steel by Jared Diamond. I think it should be required reading for every high-school student.