A moral counterexample has this structure: We accept a moral principle from a particular theory as an hypothesis. Then we examine actions, under various circumstances, demanded by the principle. If a principle clearly demands actions that are generally considered to be basically immoral -- serious moral infractions -- then the theory is considered to be disproved or else its status weakened by the counterexample. For a counterexample to be strong, the theory must clearly entail that the action is required, and the action must be widely, and obviously, considered quite wrong.
    For example, suppose a person holds a theory that all actions are morally permitted unless a person wouldn’t want it done to them. But this means that a person who doesn’t mind suffering a pain would be willing to inflict a similar pain on others. This would be considered a counterexample to that person’s theory, which is much like the Golden Rule, a biblical principle demanding that a person do to others as they would want done to themselves.