Here are some questions for the metaphysical naturalist: On naturalism (or materialism) what is it that gives human beings inherent value? Where do the unalienable rights to life, liberty and the pursuit of happiness come from? Why should we think that all must be equal before the law? What gives us the right to to be treated respectfully and justly?
Some naturalist philosophers have answered that it is the fact that human beings have "interests and desires" that confers upon them these rights, but it's a mystery as to how that could be. What does the existence of our interests and desires have to do with the obligation of others to treat us respectfully? It's hard to see what the connection might be. If one asks why, exactly, I should care about the interests of others, the answer is likely to amount to some variation of "We just should." The attempt to ground my moral duties in the fact that others have interests and desires strikes me as a purely arbitrary, and desperate, attempt to salvage human rights from the nihilism to which naturalism inevitably leads.
But suppose for a moment that we accept the answer. What follows? Are not some interests and desires more valuable than others? Is not the satisfaction of some interests and desires more worthy than others? If so, then what obligates us to respect equally the life, liberty and happiness of those whose interests and desires are less worthy?
The fact of the matter is that unless our worth and our rights derive from a transcendent source, then they are grounded in nothing. Apart from a transcendent ground we have no dignity, no inherent value, no matter how many interests and desires we have. John Locke and Thomas Jefferson both recognized this which is why both men based human rights in a Creator God.
When secularists and atheists go blathering on about human rights and equality they are like men who are attempting the intellectual equivalent of walking on water. It would pretty remarkable if they could pull it off, but we, and they, are pretty sure they'll accomplish nothing more than making themselves look foolish.RLC