We want things to be “normal”, meaning peaceful. Unfortunately our idea of normalcy is not congruent with reality, which is that mankind is violent, and will use whatever means is at their disposal to achieve their objective. If the aspiring miscreant recognizes that a target is soft, it’s an easy decision for the the I indoctrinated fanatic who has no respect for those who are not his fellow travelers . If the target is hardened then it’s a deterrent. But if you have religious fanatics who buy into the afterlife as a reward for their actions in the name of their God while on Earth, who are fed a steady diet of hatred, whose family will get blood money after they commit crimes against humanity, you end up with atrocities. Islam of course is not the only religion that has produced monsters, but it is the one producing most of them in the 21st century.