Once the claims to ominiscience and omnipotence are made, anything human, all-too human pales in impact. Likewise, mere mortal demands carry little or no influence with heavenly decree and divine dictation. It is very difficult (doomed as you say) to convince a person to challenge or reject these sort of godly governances- if they are convinced in their legitmacy and jursidiction.George: "All fanatics are dangerous. Religious fanatics are especially so because they believe the 'Truth' they claim has the sanction of a deity and therefore cannot be challenged by mere mortals. The thousands of victims of the events of Sept. 11, 2001, were some of the more recent additions to a long line of human beings who have been sacrificed to such 'Truth' by those who will permit no deviation from it." (p. 45)
You may think there's no benefit in drawing the distinction. I do. Once a person claims to be committing violent acts on behalf of a "God," then any attempt at rational discourse is doomed to failure. Such actions are not a direct consequence of religious belief, since most religious believers don't behave in such abhorrent ways, but such actions are, in my view, dependent upon such belief, else they lose their rationale.
But I question if fanatics are really so sure of what they claim. Are they as certain as their words and deeds communicate? Perhaps there is a gnawing sense of confusion, misunderstanding, uncertainty that disturbs them very deeply. Perhaps it is their fear that they don't really believe, or believe enough, or have the true and right kind of faith...that motivates them to such extreme acts of piety. Maybe their fanaticism is a symptom of a faith losing ground, becoming pointless. It is a dangerous act of overcompensation: a desperate flailing against uncertainties and disillusionment.
I think there is some virtue in bringing counter-trajectories within a tradition to bear against some fanaticisms. If the argument involves theological interpretation and scriptural exegesis, then counter-arguments can be drawn from similar theological assumptions and scriptural references. Appeals to tradition and ritual can also provide a reasoning that is not entirely foreign or ipso facto rejected.
Arguments for a violent jihad that murders innocents can be countered with multiple scriptural, traditional, legal and moral arguments that describe a profoundly different piety and call to action. Likewise, a warrior Christ unleashing vengeance on the unrepentent in the name of National Security, can be countered by a Jesus who said blessed are the peacemakers, the poor, and those who mourn...who said to turn the other cheek, to pray for and love our enemies.