That is not true. That standard has historically applied only to people who are "in your group". People throughout history have had no problem killing a neighbo

That is not true. That standard has historically applied only to people who are "in your group". People throughout history have had no problem killing a neighboring tribe and taking over their stuff (including women and children). I doubt any poor person sees a rich person as a part of their extended social group. The psychological barrier does not exist.