The same way that Dodos are a species of flightless bird, even though there are no Dodos. The sorts of truths I'm talking about are conditional truths, of the form "if someone was happy then it would be good that he was happy", and that's true even if there are no minds to be happy.
But in a world where no Dodo's had ever existed or ever would exist, then the sentence would lose all it's truth value, because it would be utterly meaningless. "A possible world is a complete way things might have gone, past, present, and future, down to the last detail, everywhere in the universe." I don't think it makes sense to project the sense a statement makes in the actual world into another possible world where the conditions that make the statement make sense in the actual world are postulated as not obtaining.
You're presupposing subjectivism. I don't think subjectivism is a rational position to hold, not only is there no evidence for it but there's quite a lot of evidence against it (even Craig's thought experiment about the Nazi's works).
I'm not presupposing subjectivism. I'm roundly refuting objectivism as incoherent. I'm sorry if you can't quite grasp what I'm saying, but it seems so self-evident to me that it's almost difficult to put into words. But I think the thought experiment of imagining a world with no conscious subjects in it and seeing that morality would and could not exist in such a world is pretty convincing.
What you are saying is that morality would still have conditional existence in the absence of conscious subjects. But the condition that would make its existence actual are exactly the presence of conscious subjects, and that exactly proves my point, i.e., that moral values are conditional on the existence of conscious subjects, hence they are mind-dependent and ontologically subjective by definition.
I'm sorry, but that is about as crystal clear as i can make this. If you won't accept this argument, then all I can think is that there is some emotional block to your accepting it.
BTW: I'm not sure if you have noticed that I'm not a moral subjectivist. I make a distinction between ontological and epistemic subjectivity/objectivity. Just as an entity like the United States of America is ontological subjective and yet epistemically objective, i.e., it is completely possible to be factually right or wrong when making statement s about the United States of America*, so is morality a social construct that nevertheless it is possible to make true or false statements about. The fundamental principle that allows this to be the case is determined by social evolutionary imperative. So, yes it is a fact that torturing people for fun is absolutely morally wrong, by definition, but it does not require one to abandon naturalism to believe such.
True and false statements about ontologically subjective but epistemically objective facts:
The U.S.A is in Asia. F
The U.S.A has three branches of government. T
Killing people for fun is morally acceptable F
Helping your fellow man is morally good T