Moral relativism holds that there is no universal conception of moral right and wrong, and that right and wrong is relative only to the predominant culture in which an action is being considered.
Therefore what is considered murder in one culture may not be so considered in another, and moreover the act may not be judged outside of the cultural context in which it occurs.
I refute moral relativism with the argument that it is a self-contradictory, and thus invalid concept, since it requires and yet cannot sustain the concept of tolerance.
As an illustration, consider that in order for the notion of moral relativism to hold, a universal moral good is required, that being tolerance. This however, is a contradiction of moral relativism which requires that there be no universals.