The value of human life

Sometimes you read a sentence without really paying attention, nothing but a sequence of word in a context: as long as you get the general gist of it, you keep on reading. Other times though, you read a sentence and it strikes a chord, exacting a deep emotional response. This just happened to me as I was reading an article on Cambodia's Khmer Rouge regime. The article quoted the Khmer Rouge as stating, in referring to people (usually urban and educated) they perceived as dangerous : "To keep you is no benefit, to destroy you is no loss.". This sentence (in both senses of the word) hit me like a ton of bricks; in only a few words, it captured all the inhumanity of this political regime. How can a person, group, organization or nation get to that point? How can human life have so little value? Of course this is not the only example, reading this brought to mind another quote attributed to a certain Arnaud Amaury, a 13th century papal legate, who said to an army trying to differentiate heretics and catholics : "Tuez-les tous, Dieu reconnaîtra les siens." (Kill them all, God will recognize his own). How can rational human beings make such statements? How can they be so emotionally detached to not consider the full impact of their words? It's hard to say. Certainly considering the victims as a whole instead of individuals would bring some level of detachment. Also, believing that somehow the end justifies the means; thinking that a goal, what ever it is, is more important than the damage caused in achieving it.
No matter what means is used to shelter one's self from emotional involvement, it still comes to a point where people weigh human life against something else; how can that be done? How can anyone, regardless of name, rank, position or function have the authority to decide the importance of someone else's life. Would an army general risk his own life in his battle plan? Would a judge hand out a death sentence if he was himself found guilty of the capital crime? Would a Health Management Organization (HMO) representative deny himself necessary life saving health care? Would an aeronautic engineer willingly get on board of a prototype he knows is dangerous?
No great answers here... just food for thought. I am not really sure a life can have the same value in every one's eyes. It's perceived worth certainly seems to diminish with emotional distance: I would be devastated with the death of one of my children yet I can hear news of thousands of children dying in Darfur and not feel the same way.