Morality with or without religion

Why should one practice immorality if he does not believe in God? It is illogical to do so out of spite for God because this would acknowledge that God exists and if so, why predispose yourself to his disfavourment instead of looking of ways to gain his favour so that he might grant you what you want? It is also illogical to do so as a belief of atheism because an atheist should be looking for ways to exercise morality without the jurisdiction of religion. Since morality brings about benefits for humanity as a whole, even if atheism was indeed true, it would have to consolidate its philosophy with morality to be practical to the world. Otherwise, it would be better to be deluded by religion than to be enlightened by an ammoral atheistic philosophy that brings nothing but a despairing viewpoint of the way the world works. Either way, one should pursue a moral life, whether he believes in God or not.