I like Castaneda's earlier books. You have to realize, he's not describing his own beliefs, but that of the Yacqui shaman (Don Juan Matus). Language was a bit of an issue, which leads to the necessity for proper interpretation. When writing about his experiences with Don Juan, he first wrote it down with complete objectivity (he was a trained Anthropologist); that's why some of it is rather humorous, because it seems so foreign to non-Indians... then, he would try to figure out the meanings for himself. I personally tend to disregard Castaneda's own interpretations, choosing to try to interpret Don Juan's teachings for myself.

That said, I think that there is some truth in that statement. Don Juan spoke of an ancient time, when terrifying sorcerers fed like cannibals and vampires on innocent Human beings. He said that's why shaman learned defensive skills, such as astral travel, etc. Otherwise, there would have been a ~complete genocide of Humans, rather than almost. He was one of the few elders who kept the memories of those ancient wars from being lost forever. I think we'd be wise to heed his warnings, because I believe that such events are cyclical, and that we are now going through essentially the exact same nightmare, just in another (what we call, "modern") time.