I’ve long considered this and there are two basic issues, the first is to stop intefering in their environment, and the second is to put our own house in order locally.
The thing we have more to fear is the home grown disaffected, now we either have to review our own moral compasses and not provide examples of why we are the devils spawn, with our open drunken immorality spewing out onto the streets night after night. Why would any group of religious types like their young to adopt our ways? Lots of them are offended by open homo and heterosexual promiscuity and all those other new benefits of having dumped our religious beliefs, easy to point at and sway young minds in an environment like Islam with the promise of a new idealistic state worth fighting and dying for. Face it only a generation ago the then youth fought for God Country and a better tomorrow.
So if you have decided to accept multi cultures, then you have not to encourage opposites nor discourage the religious beliefs of one group whilst pandering to those of another. Or provide a level playing field and ban all religion, fundamentally it is the root cause of the problem.
As to the current situation with ISIS, they are genuinely awaiting the armies of Rome and an apocalypse, if you study their teachings, which means boots on the ground, nothing will stop until they are beaten militarily.
That’s it really, now we as a society are not going to tolerate a return to puritanism or sharia so that needs explaining hard and fast and the secular nature of our situation reinforced hard. That means fewer mosques and fewer clerics, be firm, but fair, their teachings are contrary to this nations evolved state, take them elsewhere.
Or adopt and reinforce Christian puritanism and a return to victorian ideals, a little truth, honesty, prayer, and ethical conduct wouldn’t go amiss particularly amongst our ruling caste, that way no one side has to endure a different set of ideals to the other and the seeds of radicalisation cannot be planted. You can’t have it both ways or you get what we have now.