@Cad-
in my view, ethics lapse the more focused on basic personal needs an individual becomes due to circumstances. I think the bulk of non sociopathic people would agree that torture is bad, but the minute 9/11 happened and a bunch of sheep felt fear, they justified it in their minds and over half the country was ready to start tasing every turban wearing guy in the nuts at Gitmo. An average person seeing a starving child will feel compelled to lend aid. Same person in the same situation but starving day to day in the middle of a food shortage, well maybe not so willing to help.
So I guess if you are arguing that personal survival is a stronger instinct than empathy in most cases, I would generally agree with you in most cases. There are still people who would dive in front of a bus to save a small child they don't know, so its not always clear cut. I think its a case of impulse decisions versus having a prolonged scenario. In a split second choice, empathy is going to win out. Give people in stressful situations a chance to rationalize shit for personal gain, especially when said rationalizations are greased by a social order with an agenda to push, then all sorts of genuinely evil shit occurs, especially in the face of a real crisis of survival.
I would actually argue that what you are describing are institutionalized hatred and bigotry being pressed into certain people in various cultures to serve an agenda. Religious institutions have done this for centuries to assert dominance over an ignorant populace. Governments have stoked hatred to facilitate certain agendas. But at a basic local level, humans are social animals (one of many) and that requires empathy to work. As hodj linked earlier, its how the first tribes were formed leading to eventual gigantic nations we now have. But as the numbers climb or resources dwindle, people become detached to the point of cruelty at times, as you stated.