One of the stupider concepts in ethics is the notion of "absolute" morality. Without further qualification this phrase is completely meaningless. Everything is relative to something; even under the most rigid notions of metaphysical realism, the truth of any statement is relative to how the world really is.
The phrase "absolute" morality becomes meaningful only when one explicitly states something that the truth of moral statements is not relative to.
For example, Einstein's theory of relativity states (as Minkowski showed) that the space-time separation between two events is not relative to the velocity or acceleration of the observer. The spatial and temporal separation, however, are individually relative to the observer. And, of course, the truth of statements about the spatial, temporal or space-time separation of two events is relative to the actual physical state of affairs.
Furthermore, any relatively true statement can be made absolutely true by simply including the details of the relation. The statement "My keys are in my pocket" is, for instance, true or false relative to time (sometimes my keys are in my pocket, sometimes they are not). The statement, "My keys are in my pocket at 8 Jun 2008 2:49 PM" is absolutely false (they're on the dresser). And, of course, even the most "absolute" statement about where my keys are is true or false relative to where my keys actually are. (And we won't even think about the meanings of the individual words that appear in the statement.)
These points may seem pedantic, but so many complaints against atheist, humanist, and other philosophical ethics trade directly on the ambiguity of "absolute" and "relative". The charge that atheism fails to deliver "absolute" morality is simply meaningless without further clarification.
There are two kinds of "absolute" (in the sense of "not relative to") that we can reasonably guess theists typically mean by this complaint: not relative to time and place (i.e. universal), and not relative to individual opinion (i.e. objective). The charge is more precisely stated, then, that atheism fails to deliver moral realism.
The notion that atheism cannot possibly deliver moral realism — that universal, objective moral truth is analytically (i.e. by definition) precluded by atheism — is completely retarded. Atheism easily accommodates our ordinary notions of objective, universal laws of physical reality; there's no reason that atheism would analytically exclude moral realism. If some evidence were most simply explained by moral realism — just as the evidence of our senses is most simply explained by physical realism — then atheists would be moral realists.
The charge, however, that moral realism fails to most simply explain any evidence is, however, not retarded; indeed, I would actually agree. But what of it? If moral realism fails as an explanation, then it fails. The theist's charge is then not that naturalism fails to explain something, but that there is nothing for a subjectively preferred explanation to actually explain.
That's moral subjectivism with a vengeance!