Felix said:
I suppose what I'm trying to say is that I have no idea what "subjective Good and Evil" means, if Good and Evil is decided by the individual and not the act.
It's important to remember that while "Good and Evil" may be "decided" by the individual, this "decision" (at least for some subjectivists) has more the character of
recognition than a conscious act of will.
People who argue that morality is subjective need not suggest that people just wake up and decide one day, on a whim, that X is good and Y is evil. Rather, our natures, our cultural environment, and other factors mold our moral perception of the world in a way that is subjective--that is, it exists only in our particular minds, and not as an objective quality of the action--but not consciously chosen.
For instance, if I were to ask someone "Why do you think callous murder is wrong?", she would likely say something to the effect of "Human life is valuable, and should not be extinguished except in exceptional circumstances, if at all." For the moral objectivist, this reason must be founded in some objective standard--say, reason. For the moral subjectivist, there is no "objective standard", and these sorts of reasons are always ultimately founded in subjective opinions regarding what is "right" arising from our natural sentiments and our cultural background. They do not conform to any standard independent of our subjective opinion, but we do not "make them up" either--we cannot change them on a whim for convenience's sake, because they are built into how we perceive the world.
To bring in the subject raised by the OP here, the D&D universe is not
entirely antagonistic to subjective morality, though there is something of a tension there. After all, there is no compelling moral reason for a person to do what a solar thinks is good, or what will get him a positive result on the "detect good" spell--these are not, after all, the reasons upon which we do good in the real world. So a person could conceivably have a view of morality quite distinct from that of "cosmological good" without being "wrong" from an objective standpoint--unless, of course, there is an objective moral foundation for what a solar thinks is good beyond the solar's opinion.
Plato, speaking as Socrates, asks in the Euthypro whether the gods say something is right because it is right, or whether something is right because the gods say it is right, and something of the same problem exists here--is objective moral good determined by cosmological good, or is cosmological good itself founded upon objective moral good?
If cosmological good determines what is said to be objective moral good, it is difficult to see why everyone must care about "objective" moral good, even if there is a higher power who makes a moral judgment between balors and solars... and thus we might be able to say that such "objective moral good" is not objective at all. But this subjectivist/relativist conclusion is no more inevitable in the D&D universe than it is in the real world, nor--crucially--any less.
(For what it's worth, I am not a subjectivist, but a "moral realist" with strong Kantian leanings.)