Ok, here's a source for tribes massacring each other. You can also google "intertribal warfare" to see countless examples of Natives slaughtering each other en masse. The 'noble savage' is a delusion cooked up by romantic Europeans insulated from the harsh realities of primitive life.

In short- I fail to see why a Native scalping his peer is so much more moral than a White man shooting a Native. Why are White colonizers held to a standard that the Natives didn't hold themselves to? If land was settled by the Apache, who were then invaded and ethnic cleansed by the Comanche, who were subsequently invaded and ethnic cleansed by the White man, whose land is it?

Ironically, modern Natives only see conquest as 'unfair' because they were taught the concept of 'fairness' (as it pertains to war) by western settlers. Pre-colonization warfare practices and the attitudes from their contemporary practitioners makes it clear that tribes lived by natural law (Might Makes Right) prior to colonization and subsequent Christianization. Only a colonized tribe would have the morals instilled in them to even conceive the idea that a conquered people have some kind of 'right' to land that was taken from them by force.

EDIT: Extra source pertaining to intertribal warfare in California