Religious fanatics of all religions tend to call anyone who doesn't share their fanaticism "heretics". There are plenty of Protestants who don't consider Catholics Christians and many Catholics don't think Protestants will get into Heaven and lots of very bloody and violent wars were fought in Europe over that particular difference of opinion, yet Catholics and Protestants manage to live together in peace in the United States.
I'll agree that it's by no means certain that the "heretics" or non-fanatics will win out over the fanatics but I don't think that stabbing them in the back, too, because we can't be bothered to sort them out from the fanatics, either, is the answer.
If it reaches the point we don't have the luxury of sorting out the Muslim wheat from the Muslim chafe, I expect we will inflict harm on the innocent.
From their point of view they have an advantage; there are no innocent Infidels. - Tom