I just dashed off a version of this over at Jason Rosenhouse's EvolutionBlog, which is an excellent site in support of evolutionary theory against the efforts of creationists and Intelligent Design warriors.
The subject matter was the ongoing blogosphere debate between Sam Harris and Andrew Sullivan, two intellectuals whom I have a lot of time for, about the reasonableness of religious belief. Sullivan has most recently defended his theistic belief on what are, as I understand them, essentially fideist grounds - this belief has been fundamental to his thinking for longer than he can remember, and is (for him) simply not revisable under any circumstances. At the same time, he cannot support it with evidence that he would expect to be convincing to anyone who lacks it.
One person responded to Rosenhouse's commentary on all this with the observation that we apply standards of empirical evidence only to science; we don't, for example, apply them when we make assertions of moral or political principle, such as "I have a right to participate in government."
I think that this is incorrect, and importantly so. It may describe how people actually behave, but such assertions about rights are indeed fair game for sceptical scrutiny. Indeed, if they are understood in a certain popular, "objective" way, they are simply incorrect.
I'll pick up the story from here (somewhat re-edited for a different context and to sneak in some improvements), as I claim that this is not how the atheistic, scientifically-minded folks who tend to hang out at Rosenhouse's site should be thinking.
As a moral sceptic in the mode of John Mackie, Richard Garner, Richard Joyce, etc., etc. - I am certainly going to deny that there is any objective sense in which "people have a right to participate in their government". There may be such a right within some legal system, or even within some moral system - there's nothing spooky about legal rights or about rights that are recognised within a society's positive morality. But the idea that there "just is such and such a right", somehow built into the framework of reality, is as spooky and implausible as the idea that there is an all-powerful supernatural being floating around sustaining our existence.
Lots of people, including lots of atheists, seem to believe in these spooky "rights", and so on, for exactly the same reason that Sullivan believes in God: they were brought up in an environment where they internalised the idea, and it is now so ingrained into them that they treat it as axiomatic, and make the rest of their worldview conform to it (as they form new beliefs or revise existing ones).
That does not mean that there is no such thing as good behaviour or bad behaviour, or good or bad systems of government. There is such a thing, just as a good knife (in many contexts) will be sharp and durable, a good friend will be loyal, etc. We do have standards of goodness and badness, and they are not entirely arbitrary, because they are based on human interests (such as our interest in being able to cut our meat, our interest in all the needs that friendship satisfies, our interest in having stable societies, but not being tyrannised by arbitrary government power, etc.). However, while our standards of goodness and badness are not arbitrary, they are always relative to the framework of what we actually want or need.
To the extent that what "we" ultimately want or need may be contestable - since there is no monolithic "we", but just "me" plus "you", "you", "him", "her", "them", and so on - well, so are standards of goodness and badness. Fortunately (from my framework), most of us actually do want to reduce the suffering in the world, for example, and are more likely to dispute the means of achieving this rather than to to join Nietzsche in contesting the goal itself.
I am not proposing that we should jettison all morality, but we can always subject morality's claims to sceptical scrutiny. We should, indeed, jettison the idea that moral rights, duties, and so on, somehow exist "out there", independent of the social need to establish standards of behaviour that conduce to our interests. At any given time, the prevailing norms about rights, and so on, may have some kind of non-arbitrary grounding, but we should not (if we want to be intellectually informed and honest) think they are objective and absolutely binding, or simply "exist", in the way that is often imagined. They exist - in the restricted sense that they do - to meet serve our interests, and they are always open to rational revision.
The above is what I understand to be a way to think about such things as rights and morality within the scientific worldview, and it does indeed require evidence to support arguments for the retention (or, indeed, the abolition or modification) of particular ideas about rights, and so on. We can analyse what evidence we have about particular interests, etc., and what evidence we have about what standards would conduce to them.
Of course, we can't do this exercise all the way down every time we make any decision with a moral component. Sometimes - perhaps most of the time - we do need to act in accordance with standards of morality that we have internalised, just to save time and energy. For example, some of our political ideas are so well-established and useful that it is better in the heat of political practice to apply them than to be constantly re-examining their usefulness - I'm thinking of such ideas as freedom of speech and the rule of law, and the Millian "harm principle". But even these ideas are always open, in principle, to rational, evidence-based scrutiny, and we should feel free to reconsider them in cooler moments.
This can be a frightening way to think about morality if you love the sense of certainty of "knowing" God's commands. But it is also liberating to realise that our current standards are no more than useful, provisional human inventions that can be altered, or even replaced by something better - i.e., better for actually serving human interests and projects.
I should add (now departing further from what I said in EvolutionBlog) that the more our circumstances change - with changing technology and other changes to our physical and social environments, including our understanding of ourselves - the more pressing becomes the need to apply cool, sceptical scrutiny to our inherited morality. It is not something written in the stars or in the mind of a deity. It is something that human beings invented and can improve upon. We can, and should, adapt it to our changing circumstances and understandings.