I read something lately which basically said that the ancient prejudice that American Indians were bloodthirsty savages was wrong, but so is the modern myth that they were ecologically sound woodspirits in tune with nature. The reality is they were neither saints nor sinners, but somewhere in-between.
Apparently much of their eco-friendliness stems from their small population, rather than anything deliberate. A quick googling of the term "Buffalo Jump" will reveal that the Native Americans were quite capable of being both highly wasteful and harmful to the environment.
The modern predilection for romanticising and idealising tribal cultures has a lot to answer for. As much as I like Ray Mears, he is particularly guilty of this. I saw one episode of his where he was interviewing a guy who claimed to be a member of some tribe or another, and he was obviously 7/8ths Caucasian if ever anyone was. I guess he thought that part of his heritage was more "exotic", probably because of the aforementioned idealising and romanticising.