I would agree that humans are pretty decent in tiny communities. Scaling beyond that they are absolutely unquestionably horrific monsters. Without any doubt. And those communities are not ready to punish their own community for those horrific deeds they comitted.
I take a slightly different perspective (while sharing a similar final perspective) on the community issue. Rather I think individual choice drives people to communities that they, at least broadly, align with. So you end up with communities that are not only overly permissive towards their own, but also overly critical of those outside of it. But then as those communities grow large enough divisions start to form even within the like-minded community itself, and eventually you get a division there (that often ends in an internal conflict), and that community divides again, almost like a cell splitting into two new cells. And then the process starts to repeat once again in these new cells.
Add in cells merging every once in a while, and you have the abbreviated history of humanity in one paragraph.
