It's been a major theme at Viewpoint over the years that metaphysical naturalism has serious weaknesses when it comes to the matter of ethics.
We've argued, for instance, that no naturalistic ethics can give a satisfactory answer to the egoist who asks why he should care about the interests or well-being of other people, and why it would be wrong to put his own interests ahead of the interests of others.
A corollary of this is that the naturalist cannot gainsay the man who believes that might makes right. On naturalism there's no answer to the question why anyone who has the power to do whatever he wants would be morally wrong to do so.
Naturalists will claim that reason gives us answers to these questions but there are at least three reasons for doubting this: First, human reason is just the product of chemical reactions in the brain causing some neurons to fire which causes other neurons to fire, producing, somehow, a moral principle. But if reason is simply the result of impersonal chemical reactions, the whizzing about of electrons in the brain, then why should we grant it any authority in our lives.
Secondly, even if reason is to be trusted, reason tells us to look out for #1, to place the greatest importance on our own welfare, far more emphatically than it tells us to care about the interests of others.
Thirdly, on naturalism reason is a product of blind evolutionary forces that have given rise to faculties that suit us for survival. If so, there's no basis for thinking that reason leads to truth, especially metaphysical or moral truth. Survival can as easily depend on self-deception as it can on objective truth. As MIT philosopher Steven Pinker writes, "Our brains were shaped for fitness, not for truth."
We've also argued that no naturalistic account of morality can explain why human beings have dignity, rights and worth. If we are simply the products of chance evolutionary forces, if we are, as Francis Crick put it, ultimately "just a pack of neurons," or as Stephen Hawking put it, just "a chemical scum on a moderate sized planet" all alone in the cosmos, then where do human rights and dignity come from?
We've also pointed out that no naturalistic ethics, which by its nature excludes ultimate accountability, can have any binding force. It cannot impose objective duties or obligations. An objective duty can only be imposed by an authority beyond oneself, and a moral duty can only be imposed by a moral authority that is itself both morally good and which has the power to hold all people accountable.
On naturalism there is no such authority. Neither society nor humanity in general qualify. If they did then whatever society condones would be good and right, which means that slavery, infant sacrifice, female genital mutilation, rape, honor killings, genocide and a number of other horrors perpetrated by societies throughout history would be morally right and even obligatory.
Finally, we've argued that no naturalistic ethics can give a plausible explanation of what it means to say that a particular behavior is morally wrong. If there is no moral authority higher than the human individual then the term moral wrong is empty of any content. The most it can mean is that some people don't like it and would rather it not occur.
Thus, for the naturalist moral talk is simply so much hand waving and obfuscation. To be consistent a naturalist should simply adopt Wittgenstein's dictum that "whereof one cannot speak, thereof one should be silent" and refuse to engage in any moral discussion or use any moral language.
This, however, is intolerably stifling so, in a form of moral plagiarism, what they often do is poach ethical values from the Judeo-Christian moral tradition with one hand while scoffing at the validity of that tradition with the other.
We'll talk about that tradition a bit more tomorrow.