I think also there is one more fact to consider.
The ideology factor.
You know when a group of people that unite themselves with the notion that they themselves are the only real humans and the rest of us are just their cattle.
Then like a rancher culls his herd they do just that as they deem is necessary.
I don't think that takes any special brain waves or connections.
It is just the training they receive from birth and is enforced their entire life.
That they are the only humans, the rest of us are not human therefore there is no reason to feel remorse for wrong, because it is not wrong for a rancher to cull his herd.
That is a social problem and is probably the result of one charismatic psychopath and his "bright" idea. Never forget that the average person is a follower who doesn't develop critical thinking skills. It isn't his fault, but the fault of the society in which he lives. People will always fall prey to "groupthink."
Governments and their controllers do not want people to think, only comply. There is little incentive to instill critical thinking skills in the average person, so charismatic Hitlers can and do and will continue to push societies in evil directions.