Would you consider yourself a moral relativist? Do you believe in absolute morality? Is it your position that there is a single, absolute, and "true" moral standard?
Err... It's almost impossible to judge which booby-trapped fallacy to answer first, so I'll answer then as I see fit, without trying to anticipate your next fallacious move.
We have apparently defined morality as something that makes society perform better. Any act which apparently makes society perform better (in that culture's opinion), is usually considered to be "moral", whether it actually makes society perform better, or not. Child sacrifice is sometimes considered moral, (cf Judaism) if it is thought to benefit society. Soldiers at war (nearly) always consider themselves to be moral, and sacrificing for their tribe, no matter what barbarity they commit (cf Judaism).
Execution of murderers is thought to help society, but some do not agree. Some moral quandries often start "Would you sacrifice 10 people to save 100", and people often have a great deal of difficulty answering, because they are torn between an idealised absolute "morality" for which they have no real basis, and the tribal survival imperative from which the morals were actually derived.
The constraint for deriving what we consider to be morality, is that we are playing the game of life. In order for the tribe and species to gain ground against another, it must conserve itself, but leave room to attack another tribe, or species. You will notice that Christian morality leaves room to kill as many animals and species as we like, and Christians have no problems going to war to kill other tribes off, and there is no prohibition on slaves or torture.
Your question is based on a fallacy, because morality is both absolute and relative. In order for a species and tribe to survive, it's necessary to have an absolute order: "Thous shalt not kill, unless it's people the tribe doesn't like, or wants to get rid of, or animals". Disposing of criminals and other problems, tends to help with tribal evolution, since it eliminates schizophrenia and depression from the gene pool. We can't go around killing each other willy nilly, or the city will look like the set from Evil Dead, within 2 days. Then the neighbouring tribe, who had the "no kill" rule, will replace us.
Those on Easter Island could have done with another moral law: to not cut palm trees down. That is a moral rule that they desperately needed, but obviously could not agree on.
Yes, I'm a moral relativist, if it means that I do not abhore those who worship on a Tuesday. *shudder*. Yes, I'm a moral relativist on the sex before marriage issue, or any other Christian crap.
Moral cross-cultural "absolutes"
are derived from life's demands. If you consider that God created life, then you could loosely say that God created morality, but only indirectly, by creating the implicit rules of life
Nobody is actually in contact with God, so apparent cross cultural absolutes must
be derived from common-sense, after playing the game of life. Anything which appears "relative" is because some cultures have a different perception on what fine tuning must be done. This is reflected in abortion and torture.
Now, it is not up to you to fault the above part of my argument. It's up to you to demonstrate that morality cannot be derived intellectually.
I'm simply arguing that morals can be constructed by tribes who survive, and tribes who survive will tend to use the same method, by convergent evolution. You have to demonstrate that what you perceive to be a cross cultural absolutes cannot be derived by common sense or survival imperatives
. You also have to demonstrate that it can't be done fallaciously, as well. What I mean by that, is that there is no particular reason why we should bother at all. Christianity says 99% of us are going to hell, so it should be moral to kill all of man, but we don't, for some reason. Obviously, our morals construct can be derived fallaciously as well. Why do animals bother? Something pushes them on, illogically.
If that's all too hard for you, then explain to me why you think it's bad to wake up in the morning and go out and kill people and eat them. If you actually can explain this to me, then congratulations, you have a cerebral cortex. If you can't, then the morality must come from God.