Gatsby wrote:
I suspect that it's an ages old survival instinct, the more that you fear an adversary,
the greater the need to not just defeat, but totally destroy that adversary.
As in WWII, only unconditional surrender was acceptable.
I think it was in the movie Shaka Zulu where the main character said something along the lines, " Never leave an enemy behind or he will rise again to fly at your throat ".
History has proven those words to be true.