Monotheistic religions are often based on the dogma that God created the world and mankind. This is quite a totalitarian view. If mankind would be designed with a purpose by a God, it would mean that somewhere out there is some kind of conscious super-being who is in control of all he has created. A giant master of puppets. Consequently it would also mean than nothing can be bad or good because mankind would be nothing but a puppet whose strings are being pulled. There would not be any sins that can be repented, because those sins could only be initiated by the Maker himself. Mankind would not be responsible since it only carries out orders and instructions from above.
If there is God being the creator there is no freedom and responsibility since the maker of everything is in charge. Existence then is rather reduced to being one of Gods toys. There actually could not even be a heaven and hell since it would be utterly unfair that the maker would send some of his disciples to hell and some to heaven on base of deeds that he has initiated with his godly will.
But what if there really is not such a God, no Maker? Nothing at all could be created. It would mean the universe was and will always be there. Mankind would be free. At least free from God his dictatorship. Without God there is no – by religion dominated – moral system. Either God exists or there is freedom.
But this kind of freedom actually could become pretty dangerous, which after all is the reason why religion was invented and institutions like society and culture were created. Just imagine every individual would be licensed to live according his individual fantasies…
Limitless freedom also often leads to emptiness by constraining the individual of having a purpose, of having roots. Emptiness can drive people insane.
Maybe it is the danger of the intellectual capacity of mankind: it can either create lies and those lies being repeated enough after some time become consoling truths. Or it can destroy those so called truths through its reasoning capacities. In that case only meaningless and emptiness is all that is left.
So in both ways if mankind allows the intellectual capacity of its mind play its games, life is robbed of its significance: with God it is a puppet, without God it is a temporary phenomenon. With God mankind is on a stairway to an imaginary heaven, or on a road to an imaginary hell, without God mankind is on a road to nowhere.
In this nowhere of transience – or call it existentialism – the danger of emptiness and subsequent insanity is included. One of the main reason mankind always looked for the mysterious Sugarland Country – the Life After, promised by most religions in return for obedience to their rules and restrictions in this life time.