That's how they rationalize it. The question is how did they decide to begin the terror in the first place? I find it more likely that the motive comes first and then the religion is interpreted to defend the action.
Quite a common thing in religion.

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"Man lives in the sunlit world of that which he believes to be reality. But unseen by most is an underworld, a place that is just as real... but not as brightly lit... A DARK SIDE!"
-opening from Tales From the Darkside