Yeah, ISIS is nuts; they are also filthy, amoral murderers. But there is a method to their madness here. A slice of today's liberals will pick up on the "crusader" thing, and attempt to defend ISIS's actions.
And a much bigger slice of the Arab street will also go along with the "crusader" thing.
As a side note, Eisenhower called his offensive in Europe a crusade.
And after 9/11 Bush II repeatedly called the coming American response a crusade. but he backed off of that after he was told that some people would be offended. He should have said instead, "Hell, yes, it's a crusade."
It shows how much the protective vengeance of the Lord (which Christians know) is feared. The only way a party like ISIS can head it off is to pull various satanic con jobs on would-be believers.
Turning the other cheek was never intended as a collectivist command unto group suicide at the hands of an implacable horde — this is intended as a continual inter-Christian forgiveness. Situations calling for crusades are where “love your neighbor” is more important, and where the sword bidden by Christ could make sense.