"You could tell them that a definition of "right" and "wrong" is a definition established not only by time, but also by simple geography. You could allow them to notice that some activities on your planet (prostitution, for instance) are illegal in one place, and, just a few miles down the road, legal in another. And so, whether a person is judged as having done something "wrong" is not a matter of what that person has actually done, but of where he has done it."