The stage that Muslim extremists play upon is the backdrop of Islam, whilst there may well be good players, the script of the play is interpreted by the directors, and the intent of the whole has actors in differant roles, and yet the common theme is that the directors interpret the script in their own way, and consistantly this in Islam leads to extremism.
You may well state that certain aspects of Islam are not there in the Q’ran, it does not matter one bit if this is the case, it is what the followers do in their actions that matter.
Many of these extremists only read the book to confirm their bias and prejudices, not to look critically, indeed the way they are taught the book is not one of critical analysis, it is one of rote learning, and whilst they do this form of learning, they also learn that their opinions are recieved and not self developed, they become practised in being told what they must think.
In any case, if one holy book states that the rape and murder of young girls is acceptable, that still does not make it so, no amount of justification from the scripts will make it so, but the obvious flaws and immoralities contained in these works are partly the basis of the opinions and behaviours of these people.
You also have to think about the societies that spawn these religious crazies and ask yourself just how mainstream some of the lunatics are, the advocacy of the murder of apostates for example, or the murder of a state governor in Pakistan, which has actually been supported by many religious zealots there - he was murdered for daring to advocate greater freedom for women.This is not some lunatic fringe here, its pretty much the accepted belief.
I can’t imagine any large scale religious groups whose senior leaders either approve or completely acquiesce to the murderous opinions of their followers, yet it happens in Islam all over the world. Any such religios leaders would also deserve to be condemned for such abrogation of moral responsibilities.
Currently Islam is sick, there are plenty of other things wrong in the world too, I can complain about globalisation, or consumerism, or many other things, still, Islam should not get a free pass, Islam is at the root of much extremism, and for every extremist, there has to be fertile ground in the form of a population prepared to do little, or even actively support or mould these killers.
I can’t recall an intance of moderate extremism, people murdering others for the right to live and let live.