A framework and common understanding of what is right and wrong allows individuals to live in harmony with one another. Since humans are social and rely on each other in a material sense, it is in our best interests to help one another and conform with agreed to norms. Non comformity with important and commomly agreed to rules of behaviour is normally not reinforced (especially in the short term). It should not matter if the community is made up of believers in a God, non believers, or a mixture.