As a biologist, I see belief in God-given morality as American's biggest impediment to accepting the fact of evolution. "Evolution," many argue, "could never have given us feelings of kindness, altruism and morality. For if we were merely evolved beasts, we would act like beasts. Surely our good behavior, and the moral sentiments that promote it, reflect impulses that God instilled in our soul."
Nor should we worry that a society based on secular morality will degenerate into lawlessness. That experiment has already been done — in countries such as Sweden and Denmark that are largely filled with non-believers and atheists. I can vouch from experience that secular European nations are full of well-behaved and well-meaning citizens, not criminals and sociopaths running amok. In fact, you can make a good case that those countries, with their liberal social views and extensive aid for the sick, old and disadvantaged, are even more moral than America.