It would be unfair to liken our home-grown Christian fundamentalists to the kill-crazy fanatics of Islamic State who inflicted death and terror on Paris last Friday night. But the groups do have beliefs in common: that truth is to be found not through rational inquiry but through faith in the one true God; and that the terrors of the earth unfolding around us are signs of the imminence of the day of judgement.

There are other, related similarities too. For example, just a couple of centuries ago - and a century is not a long time in religion - infidels and apostates were being crucified or burned at the stake by adherents of both belief systems.

So the political leaders and commentators who assert that IS cannot be a truly religious organisation because of its cruelty show a certain ignorance of religion. "Islam is a religion of peace," says Barack Obama. Who told him that? Not a Koranic scholar, anyway.

We are invited to believe, too, that Christianity is a religion of peace, notwithstanding the imperial legions slaughtering their way across continents to the tune of "Onward Christian Soldiers."

Three times a day, devout Jews recite: "May the One who causes peace to reign in the high heavens, let peace descend on us, on all of Israel, on all of the world, let us say, Amen." To which we can only respond: tell it not in Gaza.

Buddhists are widely admired for their smiley, contented approach to public affairs. But Burmese Muslims might take a different view. In recent times, militant monks have led Buddhist mobs in mass assaults on their Muslim neighbours, for no reason other than religion. Two years ago, at least 40 Muslims, including children, were beaten to death by Buddhist extremists armed with clubs in the market town of Meiktila. Seventy Muslim homes were burnt out in Oakkan after a Muslim girl on a bicycle bumped into a monk.

Most religions most of the time claim to teach peace. But when conditions for violence arise in the surrounding material world, religion is commonly deployed to justify extremes of violence which it would be impossible to defend in secular terms.

Faith in the one true God can cover a multitude of sins.

For many in the West, the intensity of the cruelty of Islamic State was measured when gay men were hurled from the roofs of buildings in Mosul. What perverse view of religion could sanction such atrocity? Perhaps Leviticus 20:13? "If a man lies with a male as with a woman, both of them have committed an abomination; they shall be put to death; their blood is upon them."

But Christians wouldn't behave like that today? Google Uganda.

Stoning women to death for sex outside marriage? Deuteronomy 22:13-14: "If any man takes a wife, and goes in to her…and evidences of virginity are not found, then they shall bring out the young woman to the door of her father's house, and the men of her city shall stone her to death."

Christian men don't stone women to death for sexual misdemeanours any more. But it was only a generation ago in Ireland that "fallen women" were sentenced to living deaths and their babies sometimes done to death for the crime of having had sex outside marriage.

Christians shouldn't get too high and mighty about contrasting their own beliefs to the atrocious acts of IS. There are other sections of society - irreligious people, for example - better placed to offer judgment.

Fundamentalist Muslims and Christians both believe that the final battle between light and dark is coming soon and will be fought either at Dabiq, near Aleppo, as IS would have it, or at Armageddon, about 50 miles north east of Jerusalem, as the bible-and-thunder faction insists. When the day comes and battle is done, the good will be raised up, the accursed cast down.

When you think you know that's the day that's dawning, staying the blade from the apostate's throat makes no sense. Might even itself be a sin. (This is one of the key differences between IS and Al Qaida. Bin Laden had no time for millenarianism.)

None of this is to say that religion is the only or main factor in generating the unspeakable cruelty on show in Paris last Friday. It is to say that the claims of IS to represent a genuine religious tradition cannot be dismissed out of hand.

It is also to say that, all things considered, we'd be better off without any religion at all.

Belfast Telegraph