Do "Universal Rights" Exist?

I started thinking about this yesterday when I was eavesdropping on a random conversation at Houlihan's. One party was claiming that "people don't have the right to tell countries what to do" or something along those lines. However inelegantly expressed, the sentiment got me thinking about the justification of humanitarian intervention and related concepts. Here in the US we "hold these truths to be self-evident..." and at least pay lip service to "life, liberty, and the pursuit of happiness". But these can be regarded as a kind of legal fiction; they're universal inasmuch as they're enshrined in our founding documents and we've all agree to play by that set of rules. They're not truly universal, though, but rather are limited in scope to that group of people and institutions which are bound by the US Constitution. So how then does one justify intervention into the affairs of a nation bound by a different social contract? To do so implies that both the intervenor and the intervenee are beholden to a trans-national set of rules. Whence spring these rules? Coincidentally, as I was writing the above words, I took a break and read this post by Ed at Dispatches. He succinctly states a (possibly the) fundamental principle of libertarianism, which seems germane to this discussion:

...each person owns themselves and has the self-determination that comes with that self-ownership.

If you accept this as an axiom then is becomes relatively easy to derive a moral system in which humanitarian intervention is justified. But, being axiomatic, its an arbitrary statement without further underpinning. I can claim that "each person is owned by their parents" or "every person owns what they can control" or any of a number of other permutations and be just as correct. When a conflict arises between different axioms how do you arbitrate that dispute? Absent any sort of voluntary mutual agreement (like the UN, for instance) it seems untenable to suggest that there's any reason to favor one set of axioms over another. Interestingly enough, this seems to be a case where the religious among us have the upper hand over the non-religious. The religious can point to their deities of choice, say "because they say so", and be consistent within their own framework of reasoning. The non-religious, on the other hand, generally have no such escape from the question. The materialist/naturalistic epistemologies that I'm familiar with accept that the physical world is non-normative and that axioms are arbitrary; such frameworks provide no mechanism for choosing one set of axioms over the other. You can argue consistency within a particular framework (like, say, Utilitarianism), but you can't provide a reason to accept one framework over the other (Utilitarianism vs. Formalism).