ABSOLUTISM AND ETHICAL RELATIVISM
According the guys whose business it is to think about deep subjects — the philosophers — notions about the nature of good and evil lie along a continuum from absolutism to ethical relativism. There are problems with both extremes.
Absolutism appeals to conservatives because it provides a clear set of moral rules. It provides certainty. But where do those rules come from? Absolutism is usually associated with traditional religious faiths, but there are many of those. Which is right? When pressed the absolutists usually respond with what amounts to "I believe because I believe and that is that!"
Extreme ethical relativism denies that there are universal ethical truths. (Actually, few people go that far, but it is illuminating to look at the extreme.) Calling something “relative” raises the obvious question: “Relative to what?” Absolutists think that relativism is like playing tennis in a dark, dense forest without a net. Unless that “relative to what” question is properly answered, they have a point. Unfortunately, some ethical relativists don't bother to answer it.
The real answer to that question depends on an even deeper question — or rather two related deep questions — What is the nature of the world? and How can we know about it?
Most people do not spend much time thinking about such questions. They just go about their business, and if anyone should raise the issue, it seems to them that the answers are pretty much obvious. But the truth is not obvious; it is just that we absorb the answers to these questions from the culture in which we grow up and take them for granted. They are unexamined assumptions.
The two dominant thought systems that control the world-view of our culture are science and the Judeo-Christian religions. The scientific viewpoint is now ascendant; even the most religious folks grant the authority of science at least in the physical realm — and that is a decisive concession. It is certainly possible to criticize the scientific viewpoint (and if you really want to go to the roots, you should), but the power of science to make sense of the physical world is undeniable.
If we assume that science is right in the main about the nature of the physical world, then we can make some tentative answers to the question “relative to what?”