Sam Harris wrote the End of Faith. Religion has plagued civilizations for eons. The biggest threat to mankind's existence is Islam. One day we will see a "believer" launch a nuclear attack on a western city in the name of Allah.
This will not be some poor slob of low intelligence, lack of economic opportunity or education. It will be someone who thinks like most Muslims that being a martyr and helping to bring an Islamic Caliphate to the world is his greatest aspiration. He will truly believe that he will be handsomely rewarded in the afterlife. Be grateful that 500 years ago the Christians did not have access to today's technology.