Why can’t I have my own definition of morality? And ‘not culturally relative’ is not specific. This snippet from Wikipedia shows just some simple variety in the way moral relativism can be defined.
The idea that people agree on any definition or basis for morality is unfounded. But clearly, two people isolated from all others concepts of morality can conceive morality in their own ways.
Tao’s Revenge, you’re trying to tie together two rather complex philosophical issues without explaining either one of them in much detail and without describing the steps that form an argument showing that your position on one issue is logically implied by your position on the other issue.
If you are familiar with the concept of qualia, you are probably familiar with “What Mary Didn’t Know,” which is the classic expression of the argument that the existence of qualia implies that some form of philosophical dualism must be true. I don’t find Mary to be a valid argument for dualism, and a lot of other people don’t either, but it’s not simple to refute. You can find lots of discussion about this end of the argument by Googling. It’s been brought up plenty of times here on this board.
The other end of your argument is that since many arguments for moral realism depend on certain forms of philosophical dualism, that if the Mary argument is correct, then moral realism may be true. There are a lot of problems here. To begin with, Mary doesn’t tell us what form of dualism is true. It isn’t an argument for any specific dualist position, but an argument against monism (and specifically physicalism). Theism, Platonism, moral realism, astrology, spiritualism, and astral projections and the theory of Atlantis may all be contrary to physicalism, but disproving physicalism still leaves you with a long way towards demonstrating any of the contrary positions to be true.
But really, the problem with moral relaism is not physicalism, but that we can’t really agree on what “should” or “ought” really means. If you accept certain premises, it’s easy to develop an objective (or a subjective) morality, but there’s always the question “What if I disagree with the premises?” Objective morality doesn’t make any more sense than objective geometry. If you start with the axiom that all human desires are, prima facie, of equal weight, and that no other desires are of equal or greater moral weight, then you will probably come up with something like what LHOD came up with. If you start with the axiom that all animal desires are of equal moral weight, you’d come up with something different. If you start with the axiom that the desires that would inhere to a hypothetical rational entity who was both omniscient and omnibenevolent are of greater moral weight than all others combined (a position that can be proposed independently of one’s actual beliefs about the existence of such an entity) you might end up with something very similar to one or the other of those positions or you might end up with something else all together. If you believe that morality is that which leads to the greatest total amount of happiness in the universe, that might prove to be very different from that which leads to the greatest number of fulfilled desires (if fulfillment of desires does not lead to happiness), and might also be very different from what would result from the position that the greatest amount of happiness per being is the goal. And of course, any criterion for choosing between axioms would itself be (or derive from) an axiom that could be accepted or rejected. This is true regardless of whether physicalism is true or not, and even regardless of whether any particular form of dualism is true or not.
Did you choose that example deliberately? If I did as I was told and waited until the man turned “blue” before I crossed the road, I’d never get to cross the road. 
Wiki definition: Natural rights, also called inalienable rights, are considered to be self-evident and universal. They are not contingent upon the laws, customs, or beliefs of any particular culture or government.
Swap a couple phrases here and there and the debates would read practically the same.
Which makes your belief in objective morality puzzling. Although I’m not sure your idea of objective morality overlaps much with what other people mean when they use that phrase.
These would be facts about why, physically, one person adopts an attitude toward pie. I don’t imagine this exercise shows that apple pie is universally the best pie, if the subject thinks so. It is not an objective fact of the universe that was waiting for humans to discover. Most people don’t think their personal opinions on food are universal truths. But when it comes to opinions on morality things change. Then they should apply to everyone, everywhere.
I’ve never read an author claiming that humans do not have morality. That would be a new discussion.
Alright, so what does then? If you reply with a list of premises and conditions you can save a lot of time and just say “I do.”
You may as well ask what my favorite movie is, and why. I have an opinion on genital mutilation for either sex. I think it should be a universal opinion. Yet I am not conceited enough to believe this is written on golden plates anywhere. It’s objectively a fact in the trivial sense I have the opinion in my skull. But of course, lots of people disagree, so that’s an objective fact of their opinions too.
marshmallow and TriPolar, thanks for your responses to my half-assed attempt at debating this – it’s true that I can’t prove there is an objective morality, so I’m retracting my claim that it exists.
I will say it is a debate I’d really love to have, though, and I suspect I may come back to it in the new year in a thread devoted to the idea with a well-thought OP of my own. I hope if I get to it, you will join in.