I consider it a good thing that most humans are willing and wanting to educate about the ills of xenophobia and other maladies. To have entire ethnic groups get wiped out is hard for me to imagine. What crazy times our ancestors lived through.
Reducing prehistoric existential struggle to "xenophobia" is really something...
If everybody were killed by spiders, would you talk about "the ills of arachnophobia"?
But when everybody were killed by invading foreigners, you talk about "the ills of xenophobia"??
This is just one study, which the website notes goes against consensus, and we have a very sparse view into ancient DNA. Just from knowing Norwegian geography, I'm rather skeptical of full-genocide theories.
This is basically all of human history. I guarantee you that whatever ethnic group you belong to, if they are the dominant group in a region, they got to be that way be slaughtering the previous inhabitants. Modern anthropology has really opened our eyes to this fact, which contradicts a lot of the post-war anthropology that wanted to say that, say, fall of the Roman Empire was mostly peaceful, or the mass disappearance of Early European hunter artifacts was merely the movement of "pots, not people". But with DNA studies we can confirm that no, it's not that everyone started using a different kind of pottery, it's that they were all wiped out by the new group that had their own styles of pottery. The men were slaughtered and women were raped. Same thing for modern day Japanese moving into the islands, or the Bantus migrating into what is now Namibia, or the Aztecs, or basically anyone else. All of history is built on fighting for land to call your own, and killing off the male population that was there before. It's biblical, even - read the book of Joshua.
To the contrary, I think our education system has so over focused on “xenophobia” and things like that that people are unable to understand the myriad other and more significant social factors that exist between human groups.