I know empathy sounds like a nothing word but you're bang on the money. Every act of slaughter was preceded by dehumanising those who would be slaughtered. Just have a look at how much effort is put into propaganda during conflict. This is to dehumanise the opposition because people need to be led into savagery. They learnt this in the first world war when they found that the soldiers were very ineffective relatively in that many of them only fired their rifles into the air for fear of killing somebody. The bullet to kill ratio was astoundingly poor so the time and motion people found a solution. Remove empathy for the opposition. This improved the bullet to kill ratio significantly.
The problem nowadays, especially in the US, is that the soldiers are psychologically trained to kill and debriefing for civilian life is not easy often leaving the individual damaged for life.
The Jews were stripped of their fine clothes and made to look subhuman so as to assist the guards to process them like animals in a slaughter yard. Remove the empathy and the path is cleared of any emotive restrictions.
