Speciesism is another major factor. Kinda the elephant in the room, in this case. I mean, people would be outraged if all the victims of these murders were human but since they're not, morality just goes right out the window. Easy to do when you happen to be the most powerful species around, I guess. People love to wax on about how good they are but at the end of the day, it usually seems to just boil down to "might makes right."