yes, this gets us into the idea of learned morals. Why do you suppose those Incans and Mayans did those things? Because their Gods demanded it from them, period.
Therefore it was the right thing to do, whether we like it or not.
They really believed that sacrifice led to reward for all, and the families of the sacrificed were heralded.
So where was your God`s morals then, which you suggest were given to everyone, without the need of the ten commandments?
Would you roll over and atribute it to Satan?
Picture snatching a newborn baby and raising him to celebrate everything morally wrong. If the baby is not raised to see the consequence of negative actions as being negative, it would be morally backwards. A good example would be the passing on of racism.
Picture an everyday child hearing some cuss word and repeating it to his parents, he sees his parent`s shock and disdain over it, creating guilt. The child didn`t know it was bad until he witnessed the negative results of it`s use. Only when he is psychologically adept at understanding what that word really meant, would he understand why it was negative.
Compare that to the Incans.
Moses was fully capable of pulling the ten commandments from his own mind. He already had exhibited emotional responses before that biblical point.