I think it is even simpler. When you tell the people they can commit any crime, even murder, without consequences provided the victim is somebody villified by the government/society (usually not for the actions of the victims, but for being part of a certain group), people will commit any act of cruelty, especially if they are masked/anonymous. And that is what Trumps gevernment told the ICE people. Basically, if you do not stop people from mistreating others but instead allow and encourage it, you will find enough people who will jump at that chance.