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:
[B]elievers in Judeo-Christian moral absolutes often assume that situational ethics is the same thing as moral relativism and therefore regard situational ethics as incompatible with Judeo-Christian morality. They mistakenly argue that, just as allowing individuals to determine what is right and wrong negates moral absolutes, allowing situations to determine what is right and wrong also negates moral absolutes.
This is a misunderstanding of the meaning of moral absolutes. It means that if an act is good or bad, it is good or bad for everyone in the identical situation ("universal morality").
But "everyone" is hardly the same as "every situation." An act that is wrong is wrong for everyone in the same situation, but almost no act is wrong in every situation. Sexual intercourse in marriage is sacred; when violently coerced, it is rape. Truth telling is usually right, but if, during World War II, Nazis asked you where a Jewish family was hiding, telling them the truth would have been evil.
So, too, it is the situation that determines when killing is wrong. That is why the Ten Commandments says "Do not murder," not "Do not kill." Murder is immoral killing, and it is the situation that determines when killing is immoral and therefore murder. Pacifism, the belief that it is wrong to take a life in every situation, is based on the mistaken belief that absolute morality means "in every situation" rather than "for everyone in the same situation." For this reason, it has no basis in Judeo-Christian values, which holds that there is moral killing (self-defense, defending other innocents, taking the life of a murderer) and immoral killing (intentional murder of an innocent individual, wars of aggression, terrorism, etc.).
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.