Past behaviour is no guarantee of future performance. The world markets are filled with people who've completely failed to heed this advice; a significant portion of whom make quite a lot of money failing to heed it. Like most absolutisms, the devil is in the details. In trying to predict how a thing will respond, context is at least as valuable as history to any analyses. History however should never be forgotten. Something I try to consider whenever I hear Christians explaining how their faith has already outgrown the bloodshed currently associated with some of the younger, more exuberant religions.
The argument goes as follows: "oh sure, we had The Inquisition, and The Crusades, oh yeah and there were those witch hunt things, but hey, that was a long time ago!" Believers will attempt to distance themselves from their own provenance, to establish that these atrocities were committed by another whole different group of Christians, who were altogether less mature, and were otherwise lacking in worldly experience. Such barbarism is completely impossible in the modern, happening churches of today. Apparently it's just a phase, something akin to teenagers and hormones. Usually religions grow out of this sort of thing.
The new God on the block
And then there is Islam. As the relatively new God on the block, (not the newest mind you, we've still got the Mormons and the Scientologists,) is Islam simply a young religion still in the throes of adolescence? Are we then required to be more tolerant of its quirks? When it misbehaves, should it be punished? Perhaps a time out. Surely once these brash young believers attain the seasoning and wisdom to better understand the nuances of their faith, they will adopt more of a live and let live philosophy toward the rest of the believer spectrum.
To be sure, most of the popular religions today vocally disparage those who continue to spread the good word via the bludgeon. Now freshly laundered, they claim the higher moral ground. But how much would it take? Religion has far more bad old days than good. It really isn't difficult to imaging rampaging Christian hoards inquisitioning their way across the world again, setting alight all the pro-choice witches, and vanquishing abortion demons; or an evangelical theocracy hurrying on the Rapture a bit so they can get back to heaven before the buffet runs out of those fiddly tiny shrimp things.
Honest, we'll do better this time.
The only thing needed to bring our less bloodthirsty God clubs back on the road to global domination is the right set of circumstances. Any major breakdown in our social fabric will do. Turn off the lights for a while and wait for the torch bearing mobs to come to the door. Conflict is the default position for any religious doctrine (no doubt a result of being the only bunch who know the truth). Most religions of the world have established a pretty awful track record of minding the store, and there is absolutely no reason to assume the same would not be true if such a disaster were to befall us again.
The effects would be quick. Chaos within days as food and water run out. Roving gangs, lawlessness, the crumbling of the illusion of control. Maybe some communities holding out for years, but in the end, darkness. For how long?
The last time the lights went out Rome was dying. It stayed dark for a thousand years. During this period, the single most potent political force remaining in the west was the Church. Let's look at the behaviour of this benevolent behemoth, during the period of history we know as the dark ages.
Who turned out the lights
When Rome fell, after.enduring a two year siege, at the hands of the Barbarians who would later come to be known as the Francs, it wasn't simply the loss of the city, it was the loss of an idea, an expectation. The expectation the world would remain as it was. The degeneration of the empire was quick. New warlords fought old warlords for territory and position. As with most conflict it was those on the sidelines who paid the steepest price; Peasant farmers toiling endlessly to wrest a living for their families from war torn soil. Intertwined with every aspect of this social degeneration, the Church plotted and schemed, supporting this faction or that in an effort to maintain access to the corridors of power.
In the formerly Roman province of Gaul (what was later to become France), a barbarian named Clovis sought supremacy through lance and sword. His armies cut a swath through the countryside, seizing any point of geography which seemed. The peasants of course presented no problem for the would be king. Other armies however were another matter entirely. Loyalties shifted with the tides. Today's ally could easily become tomorrow's aggressor. The unity Rome had forged was in a shambles. Clovis desperately needed something to bind his new people together, and to himself. He found his answer in God.
Now Clovis was not the first ruler who thought to use religion to unite disparate groups under his control. Before Rome fell, Christianity became the official state religion, all Romans were required to be Christian. This was the Church's first taste of true power, and as with most who seek power over others, they found themselves loathe to relinquish their hold on the souls of men. Sensing that Clovis was the most likely to end up holding the reins of political power, the Church made him an offer he couldn't refuse. All Clovis need do was submit to baptism and join the true church, for the religious leaders of the day to throw god's support behind his claim to the throne.
Hey, don't do it for me, do it for God!
Overnight, Clovis became king Clovis the anointed of god, and his struggle for control became a holy war against the heathen foes of the one true God. France was born, and remains a staunchly catholic nation to this day. Was Clovis required, as price of admission, to repent for his sins of slaughter, was he enjoined to beg forgiveness before being invited into god's grace? Not so much. We're his various carnal appetites assuaged by his new relationship with God and the Church? I think you can guess.
For a thousand years the mother church cared nothing for the plight of its people, focusing instead on reinforcing its grip on power. Torturing and murdering any who disagreed with their God and his teachings, while cheerfully disregarding those same teachings themselves. Heretics were imprisoned and burned, the same was true for witches. Schisms in the church led to wars between the old school Catholics, and the new fangled Protestants. Geography being the chief determining factor in deciding who was attacking whom. The birth and spread of Islam led to the crusades. The crusades gave birth to hatreds that have lasted almost a thousand years. Today's zealots don't even disagree about the one true God. They just can't seem to get the name right.