Are certain moral propositions self-evident: is it reasonable to simply assert them without further justification?
Christian apologist William Lane Craig claims that “actions like rape, torture, child abuse, and brutality are not just socially unacceptable behavior–they are moral abominations [. . . .] People who fail to see this are just morally handicapped, and there is no reason to allow their impaired vision to call into question what we see clearly.” But surely if you’re not prepared to offer good reasons for why we shouldn’t do these things–if you just want to assert that they’re wrong because they’re wrong because they’re wrong–then haven’t you just conceded the argument? After all, those who do fail to see clearly what you–what most of us–see clearly with regard to these issues: aren’t those the very people you should be trying to convince?
Frankly, I don’t like arguments from self-evidence, and I think we should be very careful with them. In logic they might be OK: “it is self-evident that all bachelors are unmarried,” and so forth. In ethics, appeals to self-evidence seem to me to constitute little more than arrogant presumptiousness on the part of those making them. They’re conversation-stoppers, inquiry-stoppers, either because there are those like Craig who simply refuse to have their moral claims scrutinised (and thus refuse to countenance engagement or debate with those who would do the scrutinising), or because there are those who, failing to recognise the self-evidence of these moral claims, and seeing no other reason to observe them (since none are being offered), simply reject them out of hand. (Ergo, with divine command theory, everything is permitted.)
My own hypothesis is that the “truths we hold to be self-evident”–rape is wrong, torture is wrong, child abuse is wrong, genocide is wrong–are particularly powerful gut feelings or intuitions. They possibly equate to, or are expressions of, the “moral grammar” described by Harvard psychologist Marc Hauser: a kind of hardwired “unconscious moral instinct.” The notion of an evolutionary basis for why it is the case that we have (certain) moral intuitions is still speculative, but I suspect that if there is an explanation for why we have these intuitions, it is likely to be neurology and cognitive science that yields it to us.
Notice, though, that this would only tell us why it is the case that we have these moral ideas about x and y. It does not explain (nor does it set out to explain) why we ought to do x and refrain from doing y; why x is good and y is bad. And the argument from self-evidence explains nothing.