IV. The argument from clear casesI think this makes more sense as an argument against relativism, rather than subjectivism. I don't see how this argument can be anything but circular, though. The second premise amounts to "X is (obviously) absolutely wrong." This is just an appeal to our moral intuition that some things, at least, are really wrong, and not just wrong according to some particular standard.
1. If moral values are subjective, then even in clear cases of wrongness, we have to say that it is neither true nor false that an action was wrong.
2. But consider the case of someone inviting another person over for dinner, shoving that person into the oven, and then eating them as dinner. (Or the Holocaust, etc.)
3. Therefore, moral values are objective rather than subjective.
But that moral intuition is exactly the point in dispute: the relativist says the intuition is simply incorrect.
(We can also quibble that premise 1 confuses the issues of subjectivism and non-cognitivism. The cognitivist subjectivist, for example, agrees that moral judgements are subjective, but thinks they are capable of being true or false.)
Reppert's fifth argument is basically the same one, but turned around:
V. The argument from human rights.
1. If moral values are subjective, then there are no inalienable human rights. (A right in a moral obligation on the part of someone not to do something to you. If I have the right to free speech, that means someone has the obligation not to forcibly shut me up).
2. There are inalienable human rights.
3. Therefore, moral values are objective and not subjective.
Here the second premise is "X is (obviously) absolutely right." Again, it is an appeal to the very intuition that is in question.
Does anyone know if there's a non-question-begging way to formulate these arguments?