If no one can prove that God exists, then how can God can be the ultimate authority? When the occurrences that could be called “Divine Retribution” fall equally on the “evil” and the “innocent” it appears that the only authority of “God” is the fatwa, the inquisition and the burning at the stake. “Acts of God” rain indiscriminately on humans. Theologians cherry pick and memorialize the cases supporting their view and suppress the instances where the innocent are struck by brimstone or the nasty guy gets ahead.
The font of morality comes from a successful human species. What works for a society is good. What is bad for human society is in the long run, rooted out of both the genome and the society. A fixed (over tens of generations) morality is no more than a fable. The rules of acceptable behavior (morals) of the middle ages are wildly different from modern western society. Huckleberry Finn thought he would go to hell because he helped the slave Jim escape. Infanticide was the solution to deformity 100 years ago in Oceania. Jesus was crucified because he because he claimed to be the Son of God. It is no longer permissible for Catholic priests to molest children.
So much for rules: Perhaps more important, altruism is a trait which has been selected by natural selection. It does not mean that the trait is universal, but that it is prevalent in the population. Its value comes from societial benefit. Societies will usually reward altruism and shun sociopathy in its members. I know that there are scientists who argue against group selection, but there is enough evidence for it that it should be permitted as a working hypothesis
Religion and the supernatural have recorded some rules of behavior (morality) which are clearly evil. (Slavery, sexual slavery, ethnic cleansing, intent to commit filicide (human sacrifice of a son), killing of war prisoners – just in the Bible – we can find lots more in the Quran and Talmud, and that is just the Abrahamic religions).
Religion has instigated many of the worst evils on the world (9-11, the Cathars, Kosovo, Sikh pogroms, the Thirty Years War, the Crusades, Witch burning, the Inquisition, the Lebanese Civil War, the Irish Troubles etc.) all because “God told them to do it!” The fact that the Nazis and the KKK are Christian organizations has been repressed.
When a society shows children the acceptable rules of behavior for its members – that is where morals come from. Some old books serve only as props and justifications for parents and leaders who are unwilling to take the effort to search out what is important for themselves. Hewing to a tradition is easier than rational analysis. Tradition brings a stability that damps out sudden changes which may have unintended consequences. Unfortunately, religion becomes ossified – particularly when it tries to apply tribal Bronze Age morals to global Information Age life.
Religion has no guidance for morals beyond the tribe, no guidance for technologies that can wipe humankind off the globe and change the nature of what it is to be human, such as radically extended lifespan, cloning, cyborgs, gene modification, artificial life, enhanced consciousness, human actions which effect the entire world, multinational corporations, monoculture food, global climate change, WMD.
Just as important, Religion is especially blind on how to interact morally with people and sentient animals who are very different from ourselves. When the extent of a person’s actions never extended beyond ten kilometers Bronze age guidelines were OK. When the president can blow North Korea or Iran off the face of the earth with a pushbutton, we need a revision of morality – one that can be shared among all peoples. One that does not murder abortioners, stone rape victims, exterminate whales, hang homosexuals, blow up Buddhas or burn witches.