The "lined up against the wall" and "back of the head" parts may say more about the speaker than the "shoot them" part. The issue is not faith (or compassion, heaven forbid) but blind obedience.

As does the King James fealty: the "benefit" of using a translation that's at times archaic or even incomprehensible isn't unlike the medieval Catholic church's loyalty to a Latin translation: the retrograde adherents become the solely authorized interpreters.

(My college Greek was more Homeric and Attic, but I agree completely with your point.)