Reader Michael Benson responds to my post below by saying:

Personally I hold the position that it's illegitimate (from an ethical, not a constitutional standpoint) to justify one's decisions about how society should be run based on assumptions one cannot defend reasonably. As I have yet to see any compelling defense made on evidence that for example 1) there is a god and 2) that god does not want me to be a homosexual, I find it unethical to try to legislate my choice to be or not be homosexual based on those propositions. My understanding is that a significant segment of the religious right makes their case exclusively on these grounds. I take this position not because of moral relativism, but because of the lack of a reasoned argument that can be presented for the case. To the extent that one desires to restrict another based on propositions one cannot defend reasonably, I believe that one is behaving unethically. I think that legislating me based on assumptions based on faith rather than reason disrespects me as a human being capable of thought.

This could cut against someone like Martin Luther King ONLY in the event that he was unwilling and/or unable to justify his program without resorting to indefensible references to god. IE, if he was incapable of making a case through reason he was behaving unethically.

With that said, I should note that I'd be unwilling to endorse any legislation that tried to enforce this rule because I think as a practical matter it would be liable to the worst kinds of abuses. But as a principle of right action, this is what makes me believe the religious right is behaving in a way that I not only disagree with, but find morally reprehensible.

I sympathize to some extent with the correspondent's point; for instance, if we don't hear a compelling reasoned justification for a proposed law, that certainly is reason for us to reject the proposal.

But the trouble with the correspondent's broader notion -- "that it's illegitimate . . . to justify one's decisions about how society should be run based on assumptions one cannot defend reasonably" -- is that ultimately most of the moral principles that each of us has can't be defended purely reasonably. Should people be barred from abusing animals? There's no purely reasonable answer to that; at some point, it comes to down to a moral axiom, such as "people shouldn't be allowed to pointlessly inflict pain, even on animals" or "people should be free to do whatever they please with their property." And if you think this claim isn't an axiom, but can be defended reasonably through some other principle, that just means there's some other moral axiom lurking in the background.

Likewise, should abortion be legal? Pro-life people say personhood, and entitlement to moral rights, begins at conception. Pro-choice people select some other line. There's no way of proving it using pure reason; even if one makes an argument such as "a woman should be free to do what she likes with her own body" (which would, incidentally, allow abortions even at 8 1/2 months), then that becomes the axiom that you may believe but can't prove.

Or what about protecting endangered species? Many people want to protect them purely on moral principles -- humans shouldn't exterminate other species. That too is a moral axiom, or at least rests on moral axioms. Others argue that there's a pragmatic reason for it, for instance that protecting endangered species is needed in case the species may yield some useful biotech products some time in the future, or in case they fill an important ecological niche. But even such pragmatic reasons rest on unprovable moral judgments, such as that a small and incalculable chance that the species might prove useful in the future justifies the real costs to real people that saving the species would involve. Now these judgments may well be right -- but they aren't reasonably provable. And ultimately, the same is true, I think, for moral judgments even about matters such as the wrongfulness of murder, rape, robbery, and so on, and certainly for more contested matters such as race discrimination, breach of contract, defamation, invasion of privacy, moral rights in published works, and so on. All these moral and legal claims rest on unprovable moral assertions.

Of course, these assertions may be supportable, though not provable -- one can come up with plausible arguments that might influence people to accept one or another (for instance, "dogs can feel pain and emotions just like humans do, it's bad to needlessly inflict pain on humans, and it's therefore bad to needlessly inflict pain on dogs"). But these are appeals to intuition, aesthetics, and emotion. They aren't reasoned proof.

In this respect they're similar to religious people's arguments that, for instance, homosexuality is wrong because it's unnatural, and because the normal uses of our various organs reveal that God intended us to use them one way and not another way. Now the former arguments may be more persuasive to you or me than the latter. (I find the unnaturalness argument quite unpersuasive, for reasons I mention here.) But it's not because the former involved reason proof and the latter don't. Neither involve pure logic; both involve attempts to appeal to intuitive senses of right and wrong, though intuitive senses that vary among people.

So we are certainly free to say that certain arguments, whether arguments from the text of the Bible, arguments from the perceived will of God as expressed in the way the world works, arguments from church teachings, or what have you, are unpersuasive. And then if someone uses those arguments to support a law that we think is immoral, we can criticize him on the grounds that the arguments are unpersuasive and yield immoral results.

But I don't think that we can argue that the only legitimate laws are ones that can be defended using pure reason -- most important judgments about what the law ought to be ultimately rest on some unprovable moral assumptions.

So far, I've gotten about 15 responses to the earlier posts, some very detailed -- I'm afraid that I won't be able to respond to most of them, though I hope to blog a few follow-ups responding to some. Many thanks for writing!