I'm sure there is a 'turn the other cheek' clause somewhere in the Torah too. Otherwise it's time to trade it in for a new rule book. My assumption, however, is simply the refusal to heed the hard parts.
Immanual Kant ('a real pissant who was very rarely stable...') would certainly argue with your statement that killing is always an appropriate response to killing. I'm pretty sure God's not a big fan either.
The whole problem with the 'eye-for-an-eye' approach to justice is that after just two iterations, BOTH SIDES are, by definition, blinded.