It occurs to me that our behavior is not so different than animals scrabbling for territory. We wipe out, or at the very least, brand the competition as "bad," or "evil," whatever form it takes—be it other humans, animals, or plants. Thus the monikers "pest," and "weed." And we go to war on them. The strongest wins. Smarts has nothing to do with it, as we witness daily.
It's the same thing that makes a smart person continue to be an addict, whatever be his or her drug of choice.