I guess the "justifiable" killing that puzzles me is when the game guards in animal preserves in Africa shoot and kill poachers.

Granted, sometimes the poachers are shooting at the guards first, in which case the self defense idea prevails, but my general understanding is that at times the guards shoot first. The poachers are killing animals - to make a living, and the guards are killing humans - to enforce laws. Seems like the logic about the value of human life is screwy ??