A recent observation of mine is ripe for being crafted into an aphorism but I haven't been able to properly phrase it. Thusly:

People refer to another group of people as "animals" when they want to treat that group of people like animals.

Calling people "animals" is a way to shortcircuit intellectual discussion, a way to nullify and void ethical boundaries. I particularly see this in the Israeli-Palestinian conflict but I think it generally holds true on a broader basis.

An interesting variation on this is the current use of the term "terrorist" in an expansive manner to also include large groups of people who do not use so-called "terror" tactics. Anyone in armed (and sometimes unarmed) opposition may then be categorized as "deserving" harsh treatment. Thus we get a designation of "enemy combatant" for prisoners at Guantánamo Bay, a group of people supposedly outside of the legal application of the Geneva Conventions as they pertain to prisoners. Well, at least according to the current White House administration.