There is no objective moral standard by which one culture's moral code could be judge truer or better than another's. We should not judge the conduct of the people of a different culture. We should adopt an attitude of tolerance toward the practices of other cultures. Rachels argues that some of these claims are clearly correct, or at least partially correct, whereas others seem to be mistaken. What's right and wrong varies from culture to culture.
Different cultures have different moral codes.
Therefore, there is no objective moral truth. People's beliefs about what's right and wrong vary from culture to culture. What's right and wrong varies from culture to culture. The argument is invalid. It doesn't follow from the fact that people disagree about what's right and wrong that there is no objective truth about what's right and wrong.