Interesting! Your example still seems to support the thesis that pain is necessarily bad, though you have offered a clever example of when it might be good to endure that which is bad. Perhaps the original claim, then, is false if it is understood as: If pain is bad, then, necessarily, it is impermissible to inflict under any circumstances.

No, I do not think that morality is only a matter of social conventions, no more so than sickness or health. It seems to be an objective (and perhaps even common sense) fact that cancer is bad for a human being, and I think we may similarly see that rape is a wrongful violation of a person. Building on such apparent facts, one can offer what is called a natural law account of morality, in which morality can be defined (or recognized) in terms of what contributes to the flourishing or destruction of human nature. A natural law approach to morality is not the only alternative, however, for seeking to ground moral judgments. One may adopt a form of utilitarianism or Kantianism, for example. I prefer to combine a natural law account with an account of moral reasoning that highlights impartiality, an affective appreciation of the points of view of others and an awareness of all relevant facts upon which to form moral judgments. Treating morality is only a matter of human conventions seems unable to...