I've repeatedly mentioned (and cited) how much the freedom to move between groups was a part of Paleolithic life - as well as how much far flung travel took place simple for the purposes of maintaining friendships. In addition, people who actively value peace and harmony, who based their entire culture on playfulness, and who are obsessive about their personal autonomy are not then going to turn around and hurt a stranger for no reason. It's nonsensical to assert that.

Even Columbus noted how generous and accepting the Natives he encountered were. He promptly took advantage of their welcoming and friendly nature to enslave and murder them, but that's another story.

Once you start to have lands you want to cultivate as "yours", stored grain you want to keep as "yours" and possessions you've acquired, along with greater population density and social hierarchy, worrying about "the other" is more logical - although as just noted, even then it wasn't always the case. Columbus describes them as guiless and honest, kind, and affectionate.

I'll look forward to hearing more about the book after you read it, and will see if I can get to it as well, although my book pile is pretty high.