Graeber rather too often has an ax to grind. It's an unfortunate side effect of writing history from within a fixed political agenda. I've also read the memoirs in question, Bernal Diaz del Castillo's True History of the Conquest of New Spain; in fact, I first read it in my teens. It tells a much more nuanced story than current political narratives allow -- but again, I wouldn't expect Graeber to make room for that.