Dennis Prager writes:
Calling the cruelest among us names such as “animal” or any other “dehumanizing” epithet actually protects humans. The word “beastly” exists for a reason and is frequently applied to human beings. By rhetorically reading certain despicable people out of the human race, we elevate the human race. We have declared certain behaviors out of line with being human.
Biologically, of course, we are all human. But if “human” is to mean anything moral — anything beyond the purely biological — then some people who have committed particularly heinous acts of evil against other human beings are not to be considered human. Otherwise “human” has no moral being. We should then not retain the word “inhumane.” What is the difference between “he is inhumane” and “he is an animal”? Both imply actions that render the person no longer human.
I once asked Rabbi Leon Radzik, a Holocaust survivor who had been in Auschwitz, what word he would use to characterize the sadistic guards in the camp. I will never forget his response: “They were monsters with a human face.”