For centuries religion has used various natural events and objects as proof of god. The Sun, the rain, storms, plants, and the stars have been essential tools in justifying the existence of god. But as science has progressed and has been able to provide answers for many tangible matters, religion has shifted its argument to the metaphysical, mainly the question of morality. The crux of the argument is that without an originator, morality could not have come to existence. In other words there is a supernatural force that guides us towards being moral and ethical, and that force is god.
Indeed science is currently impotent to link morality with molecules and atoms, but one can argue that morality is the result of accumulated human experiences and a need for perfection. Centuries of human development has taught people that societies can better function based on certain rules and one can sum up such rules as morality.
If god is responsible for morality, why would he dictate such behavior only in the last few millennium? And why is it that the rules of morality differ so much is various societies today? Many indigenous people around the world walk around with no clothes on. Polygamy is still widely practiced around the world. Stoning and severing limbs or heads happens in many places for even minor offences. Some consider these immoral, while others do not. And if god is the origin for everything, shouldn't he be considered as the originator of immorality as well? Isn't he the creator of Satan after all? Isn't god directly responsible for death and destruction and natural disasters and famine and disease?
It seems hard to believe that without god moral people would suddenly turn into rampaging criminals, that they would abruptly turn into thieves, rapists, and murderers. I think most of us try to be good because generations of built-up experiences have taught us that civility gives much more favorable returns than chaos and anarchy.
If morality is pre-programmed by a supreme being with no alternatives, then what value can be placed on forced virtue? And what good is morality if only practiced out of fear? To quote Albert Einstein, "If people are good only because they fear punishment, and hope for reward, then we are a sorry lot indeed."