You make some interesting points. A few months ago Fox News had on a terrorist expert (an Israeli) who was talking about how to defeat terrorists. He basically said you fight fire with fire. If they kill one of yours then you don't go after them immediately. You go after their family. You kill them and dump their bodies on said terrorists doorstep. Then you kill the terrorist. I have no idea if this would actually work. Just reporting what I heard.
And you are correct in saying that America, nor our allies, have the stomach to do that.
If the motivation in doing some of this is points with Allah, we announce every terrorist killed will be buried in pigskin. If we find you buried after the fact, you will be dug up and buried in pigskin. Take some of the motivation away.
I once heard John Dean (of the Nixon administration) give a private talk where he spoke of how the Soviets dealt with Muslim Extremists. If memory serves me right, this was his story:
During the cold war, Islamic Militants captured a Soviet diplomat and held him for ransom, in exchange for money and the release of some prisoners somewhere. In response, the Soviets picked up a handful of Islamic men at random off the street, castrated them, and sent them back to their colleagues with the message "Give us back our diplomat, and don't try anything like this again." The Soviets won that exchange.
John Dean's point was that the US did not have the luxury of responding to brutality in like manner, the US public would not allow it.
Metus improbos compescit, non clementia.
(Fear, not kindness, restrains the wicked.) --Syrus, Maxims