That's a negative. A 'kill them all' strategy makes us the winners, by a mile. People just don't realize/don't remember what is possible when a war machine assumes counter-population posture, like Axis and Allies did in WWII. It was only 60 years back, how quickly things are forgotten. I *guarantee* you, make an example of *a* city somewhere, and things would change drastically. State publicly - *any* terrorist attack on US or allied European soil, and we incinerate a city with conventional weapons. Publish a list, and say we will choose at random. From my perspective, their propaganda and fascist/religeous upbringing have done far more than we ever could in order to win someone's hart/mind. That is impossible, not to mention futile and counterproductive, as Machiavelli said - better to be feared then loved. We'll never be loved. Therefore, as they already believe we're mosters out to kill them, let's play the part. One city for each act of terrorism on allied soil. I guarantee that would be enough. Random choice from a list of densely populated cities would be extremely effective as a deterrent. Number of large cities would not be able to effectively evacuate following a terrorist strike, and, it would motivate the largest number of people to stop the extremists within their own countries.
Well I can't say I disagree with "kill them all", but...even incinerating a major city to glowing embers does not take care of the other 99.5% of the potential jihadis out there in a world population of 1.2 billion(?). Respectfully, we're talking about a cult[ure] that glorifies death. And finally, couched as you've stated it, our threatened (or, executed) act of incineration would be one of retaliation, which, by definition, only proves that they are still capable of striking us. If it isn't clear, I'm not claiming to have an answer or alternative at this point. "Kill them all" still works for me, it's just that even a city's worth is far from "all".