Whether P should be trusting the oracle is besides the point.
No, it isn't. You are claiming that P "really" wants the gold to exist, but you are also claiming that P thinks that at least one of the definitions of "the gold exists" is "the oracle said the gold exists." You are flummoxed by the paradox of P feeling just as happy due to a false belief in gold as he would based on a true belief in gold, and you are ignoring the thing that ACTUALLY made him happy: which was the oracle telling him the gold was real.
How surprising should it be that ignoring the real world causes of something produces paradoxes? P's happiness doesn't depend the gold existing in reality, but it does believe on something in reality causing him to believe the gold exists. And if the gold doesn't exist in reality, P's happiness is not changed, but if the reality that lead him to believe the gold existed is reversed, if the oracle tells him (truly or falsely) the gold doesn't exist, then his happiness is changed.
I actually have not a clue what this example's connection to moral realism might be, either supporting it or denying it. But I am pretty clear that what you present as a "real mental result without a physical cause because the gold does not matter" is merely a case of you taking an hypothesized fool at his word and ignoring the REAL physical cause of P's happiness or sadness. Or from a slightly different tack, if P defined "gold exists" as "oracle tells me gold exists" then P's claim that his utility is the gold is equivaelnt to a claim that his utility is being told there is god.
Ps happiness has a real cause in the real world. Because P is an idiot, he misunderstands what that cause means, but even P recognizes that the cause of his happiness is what the oracle told him.
No, it isn't. You are claiming that P "really" wants the gold to exist, but you are also claiming that P thinks that at least one of the definitions of "the gold exists" is "the oracle said the gold exists."
I do not claim that. I claim that P believes the cube exists because the oracle says so. He could believe it exists because he saw it in a telescope. Or because he saw it fly in front of his face and then away into space. Whatever reason he has for "knowing" the cube exists has some degree of uncertainty. He is...
I figure morality as a topic is popular enough and important enough and related-to-rationality enough to deserve its own thread.
Questions, comments, rants, links, whatever are all welcome. If you're like me you've probably been aching to share your ten paragraph take on meta-ethics or whatever for about three uncountable eons now. Here's your chance.
I recommend reading Wikipedia's article on meta-ethics before jumping into the fray, if only to get familiar with the standard terminology. The standard terminology is often abused. This makes some people sad. Please don't make those people sad.