Philosophical naturalists often take relativistic views on ethics. Yet, there seems to be one ethical area about which they are absolutists, and that is the ethics of belief. They say with Clifford "It is wrong always, everywhere, and for anyone, to believe anything upon insufficient evidence." In fact, to some of them, this seems to be more obviously true than "It is wrong, always and everywhere, and for anyone, to inflict pain on little children for your own amusement."I understand where Victor is going with this - but I don't think it really works. And the ways in which it doesn't work are worth noting.
First and foremost is the escape valve: "Insufficient evidence." On its own, that's a loophole a person can drive a Mack truck through if they want to. How much evidence is sufficient evidence for belief in the existence of God? Or for atheism? Anecdotally, keep in mind a recent post of mine dealt with an atheist who insisted that belief in a negative - even a negative for which there is literally zero evidence - is A-OK. Alongside an atheist who insisted that believing something about a term which isn't even defined is A-OK. If pressed, I imagine they could argue that zero evidence for a claim is still sufficient evidence, depending on the claim. Absurd, sure, but there's that Mack truck I was talking about.
My other problem with Victor's summary is the same problem I have with the claim that naturalists have a tremendous amount of love for scientific evidence and reasoning, etc. It's a popular refrain, absolutely - there's no shortage of self-described naturalists who insist on the respect they have for science, their acceptance of it, their celebration of it. But the fact is, there's also no shortage of self-described Christians, theists, and even full-blown YECs who praise science and claim to accept science. If praise of science was sufficient to demonstrate someone had tremendous respect for scientific reasoning, we'd have to include YECs and atheists, ID proponents and Darwinists, all under the same tent. Talk is cheap when it comes to discussing one's high standards for belief, reason and rationality.
There's a third wrinkle here that has to do with the subjective aspects of having sufficient or insufficient evidence, but let's put that aside. I think what Victor is driving at is that Clifford's Principle is an explicitly moral claim - it talks about the wrongness of certain beliefs. It's prescriptive. But where are these moral 'oughts' coming from for the naturalist, especially given the prevalence of moral nihilism or relativism with regards to naturalism? If naturalism is true, believe what you damn well please, if in fact it pleases you. Reject naturalism if you like.
Now, there are potential responses here. For one, you could just deny the moral aspect of Clifford's principle and turn it into a claim of utility - 'If you wish to have true beliefs, then it is wrong to...' etc. But that leaves pragmatic beliefs untouched. True beliefs may not be valuable to you as opposed to beliefs that make you feel a certain way, etc. In fact, you can borrow some interesting pages out of the naturalist playbook on this one: 'I'm a consenting adult, who is consenting to this belief that I have. Who are you to tell me it's wrong for a willing adult to do something that doesn't involve or harm anyone else?'
There's still a move available to the naturalist: argue that, while you may be a consenting adult, your taking on a wrong or poorly evidenced belief may lead to harming others. Of course, 'harm' is going to need to be defined on naturalism (I believe this is actually ridiculously difficult to do, and ultimately requires an objective morality to take seriously), the moral status of harming others will need to be defended - and this also opens the door to questioning areas that many naturalists previously regarded as off-limits (It turns out what people do in the bedroom IS, in principle, everyone's business - at least if they have beliefs about the morality or immorality, the harm or lack of harm, of their actions.)
Anyway, just some comments on the always thoughtful Victor Reppert's thinking. Make of it what you will.