I confess to the charge of snarkiness, although I absolutely cannot recall any Islamist restricting himself to mere bloodless snark, as contrasted with holy book affirmations and bloodshed.
That's the point of contention. A Christian does something because his understanding of God's will leads him to it, and if whatever it is doesnt work out, he collapses into a paroxym of doubt and self-examination. A Muslim does it because Allah commands him to do it, and that command in and of itself makes what he does right. That's why you cannot reason with Islamists.