For as long as humanity continues there will always, at some place and point in time, be someone, somewhere willing to murder a complete stranger for no good reason. There will typically be a stated purpose, though not every time, and any ‘reason’ given can be relied upon to constitute little more than mere pretext. This will always be so. There is nothing about it that should, by the rest of us, be regarded as shocking or newsworthy.
Taking the case of the current generation of Islamist extremists toiling away in Iraq/Syria; what you have is a group of like-minded persons who hate themselves and hate the world and desire, above all else to murder and maim and spread misery. When it comes down to it their alleged ‘ideology’ is merely a shroud, behind which organization, fear-baiting and recruitment opportunities may be more effectively carried out.
But it is precisely because of the need to operate under the pretext of a higher ‘ideology’ that the battle is, principally, one of ideas. This doesn’t rule out the need for direct and measured action, where warranted. But above all, the response from civilized persons in all places where the group seeks to engage in public discourse and propaganda is to ask a single pointed question:
“How does converting the rest of us to your version of an Islamic State make the world a better place?”
It is a simple question and all non-members should relentlessly insist on knowing the answer, because any worthwhile or would-be noble ideology is able to offer a straightforward and equally compelling answer. If a straightforward and compelling answer cannot be given then the supposed ideology is exposed as nothing other than mere pretext for violence and misery and the movement, along with its members and supporters are deserving of nothing more than ridicule, general disdain and whatever else may be needed to minimize the effects of their efforts.
[EDIT] Though it probably cannot be overstated that the general ideology of love, genuine-ness and inclusion are powerful counter-forces against the superficial appeal of power, subjugation and violence. Indeed, a question to ask ourselves is what alternatives are we offering to those looking at both sides of it?