Basically, the way I see it is this: there's a pool of "already radicalised" people - and you're right that in many cases those people won't be reachable through alliance and dialogue, though not in all (to take a non-Islamic example, look at the number of ex-IRA leaders who are distinctly not blowing people up in Stormont, sure NI is still a mess but it's nothing like as bloody or dangerous as it was). However, the pool which you seem to be half denying the existence of is the "potential radicals" - mostly male, mostly young, people with relatively few life prospects given the war-torn state of the modern middle east, people without a say in their society. These are the people who ISIS want to reach out to and radicalise as fighters or terrorists. If these people have more stability in their life, better opportunities, more democratic rights, etc, they are less likely to feel like they desperately hate the world so much that they're prepared to blow themselves to pieces, or indeed harbour/quietly accept those who do.
People aren't born radical - and as you yourself noted, this is a long term fight. The key aim in terms of safety is to make radicalism less normalised and less acceptable among ordinary populations in the Middle East, to drain out the flow of manpower that fuels terrorism. Even if I didn't give a damn about the people of the middle east (which I do, because as much as I feel a very strong affinity for my country I don't think an accident of where I was born geographically should dictate my basic moral stance towards a person), it would still in my view be mind-numbingly short sighted not to think long term about how we can decrease radicalisation. Enforced occupations beyond a certain point just don't work towards that end, for most of history occupied states have just been a continual bloody mess to try and keep a vague level of control over. Bombing only works if you're literally conducting a mass extermination or terror campaign, which I've outlined my concerns with on sustainability grounds (though as I'm sure you know I'd also consider the death toll unacceptable). Without those two legs, the general population has to take centre stage, because it (and particularly its younger part) is the basic pool both of potential radical support and potential western support in years to come.
So what does work? Having people who are on their feet and able to decide about their own future, having leaders in these communities who can see the benefits of people not killing each other and will act to nip radicalism in the bud, and in the case of groups like ISIS or the Taliban removing their legitimacy by ensuring that a workable civil society is able to provide law and reasonable justice without corruption. The Taliban managed to hold territory for so long after 2001 partly because their Islamic courts are far less corrupt than Afghan ones - which is changing, but it's a slow process and one we didn't spend enough time working on. Similarly, we should've spent more money than we did (and we spent a bit, but nowhere near enough) on providing jobs in frontier areas to give young men better alternatives to running around pointing guns at people. In the case of failed state situations like Yemen or Somalia, we could be doing a lot more to strengthen those elements of the system that are working, particularly in terms of getting the economy more functional - all these things reduce the manpower and sympathy that terrorist leaders get.
EDIT: also I might call this one a day here, I think we're getting to a stage where we're both butting our heads against a wall owing to our different ideas on who it's worth treating as a fully fledged member of the human race and stuff like that. Also I have a hellish cold and am not in the right mood for this (sorry!).
