Because religion combines dogmatic certainty with the existence of the afterlife, violence and death is all too easy to justify  Particularly in the case of contemporary Islam, although other historical examples could be referred to, the combination of certainty and the promise of life after death is a sure route towards violence. That said, Catholics and Protestants in Northern Ireland demonstrated this until recently; the Yugoslav wars between Catholics, Orthodox and Muslims, both sides of the battle for Israel/Palestine and many others in history could also be thrown into the mix.  Allowing people the opportunity to claim that “God’s on our side” can be used to justify anything, especially when He appears to be fighting on both sides.