Can you argue against a moral absolute by saying yes it's rational, because it's true, but not practically so?
So can you, in principle, coherently claim that it is true that not lying is good, and so the obligation not to lie is rational, but sometimes it is rational to lie?
I hope so, though I'm probably wrong.
Perhaps practical moral skepticism can account for it being moral to lie to save the fugitive, but in this instance there's no rational need to be moral. Wouldn't that mean lying is irrational but not practically so?
As to why believe (at all) in practical moral skepticism, couldn't something like 'relevance' temper the irrationality of moral actions? A watertight mathematical proof sounds supremely rational, but sometimes irrelevant, and so sometimes it is irrational to work on it. Why not, analogously, performing moral actions?