In other words, if people can't agree on what the source of moral truth is, there's no way they can agree on what the nature of that truth is? I very much disagree.
See, now I'm reading this and wondering what we're disagreeing about in the first place.... ;)
Aside from what I stated above, what I think we're disagreeing about is that you, I think, seem to be saying that the axioms we should start with can themselves be determined by reason. Alternatively, you might be saying that they're something we should just pick out, the way one picks out a new dress style. Either way, I don't think you seem to be agreeing with me that the axioms exist as matters of truth, and that it's simply our job to make sure we know that truth.
What I'm saying is that your presumption of what universal truth is, is necessarily predicated on what you think has been given to you by a particular deity. And when what your deity says conflicts with what someone else's deity says, you're at an impasse with no clear resolution. Consider what I said about abortion earlier - either elective abortion is a wrong, as a matter of fundamental universal morality, or it is not (setting aside the notion of situational ethics for the moment).
Now, there are lots of people who are convinced that it is a universal truth that elective abortion is morally wrong. And that presumption of truth is predicated on a particular worldview, a particular notion of what God says about right and wrong. But the Jews, their God says otherwise. They don't share that belief that God says it's always wrong, so they don't accept claims about the universal truth of the proposition that says that elective abortion is a moral wrong.
It won't always be the case, but clearly, unless there is agreement on the source of the universal truth, there will not be agreement on what that universal truth is - what God says to Christians is simply not going to coincide always and everywhere with what God says to Jews and Muslims and Hindus and whatever. God says one thing to you, and quite another to them - who's got the universal truth? You? Them? Someone else entirely?
Alternatively, you might be saying that they're something we should just pick out, the way one picks out a new dress style. Either way, I don't think you seem to be agreeing with me that the axioms exist as matters of truth, and that it's simply our job to make sure we know that truth.
What I'm saying is that it doesn't matter whether it's a universal truth or not - you can't ever really know if some proposed moral principle is a matter of universal truth. There is simply no objective way of determining whether my pronouncements are universally true, or just my particular opinion. So why behave as though you can know something you cannot?
Okay, you say, we look within ourselves for the truth. Which, it seems to me, sounds as though we judge for ourselves the rightness or wrongness of some proposed universal truth, and then proceed...by consensus? ;)