Just to make sure I understand your position: Imagine two universes U1, and U2,like the one in my original post, where P1 and P2 are unsure whether the gold cube exists. In U1 the cube exists, in U2 it does not, but they are otherwise identical (or close enough to identical that P1 and P2 have identical brain states). The Ps truly desire that the cube exist as much as anyone can desire a fact about the universe to be true. Do you claim that P1 is better off than P2?
So would you argue that P2 shouldn't investigate whether the cube exists, because then he would find out that it doesn't and thus become worse off?
Yes. P2 finding this out would harm him, and couldn't possibly benefit anyone else, so if searching would lead him to believe the cube doesn't exist, it would be ethically better if he didn't search. But the harm to P2 is a result of his knowledge, not the mere fact of the cube's inexistence. Likewise, P1 should investigate assuming he would find the cube. The reason for this difference is that investigating would have a different effect on the mental states of P1 than it would on the mental states of P2. If the cube in U1 can't be found by P1, than the asymmetry is gone, and neither should investigate.
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.