The evidence shows that it is not what one believes, but the strength of the belief that matters when it comes to morality and spirit. There are saints in all religions.
Good and evil can both exist if you believe strongly in either. God will exist or not for you, because you believe or not, and you can either be mortal or immortal.
If you truly believe you will cease to exist at physical death, then the symptoms of your belief will manifest.
Imagine row on row of 'immortals' lying 'dead' for eternity because they are filled with the conviction that nothing else is possible!