Humans are too arrogant and fragile with their own mortality to believe we are not special enough to not have an afterlife or supreme being watching over us (never mind the arrogance that in this entire vast universe, our crappy little planet is the only place where life exists). It is a crutch used to justify their existence and actions, as well as to hide from their fears. Organized religion exploits this part of human nature, and is the ultimate form of population control.
