Viewpoint has frequently observed that in order for there to be any meaningful morality there must be a transcendent moral authority. Otherwise, each person simply decides right and wrong based upon his or her own preferences and predilections.
Dennis Prager has an interesting piece on this very topic in installment XI of his excellent series on Judeo-Christian values. One point Prager makes that is of some interest is that:
This will upset some who recoil from any suggestion that Christian ethics can be situational, but I think Prager is correct about what he says here. Even so, the important point is this: The choice people make as to how they should live is purely arbitrary unless they are following the will of God. If there is a God there is right and wrong. If there is no God then right and wrong are almost completely meaningless terms, and those who believe that God is irrelevant to our everyday life could not be more wrong.