then how would you define good? if there is no God or the Bible (who set the laws of what is good and bad) then we couldn't never question a dictator or murderer. Hitler would have been justified by society for doing what he did.
People know in their hearts the difference between right and wrong. They don't need the threat of a vengeant God to know how to act. I suppose an early 20th century conception of science which tried to view things in a narrow "survival of the fittest" framework might have tried to exclude moral behavior as irrational, but people who don't believe in the metaphysical are as likely to be good as those who go to church.