Whenever I have encountered any ethical proposition I find that atheist and a theist view it differnetly. I am not sure whether this is same issue of ought vs is.
To me as an enquirer after truth I parapharse the Sagan Feynman staement as : I want questions that need answers and not answers that disallow any questions.
Consider the statement “Thou shall not lie” , Is this a proposition whose truth value has to be determined or is the TRUTH. In the first case I can raise questions and then try to answer them. Within these questions may lie how science may attempt to create process of determing the truth, In second case there is no question. All is told. It to be Ought. Hence no questions so no answers mere blind following.
“One ought not lie” is a statement that is morally relevant as it serves (or fails fo serve) peoples interests (good, positive life, welfare).
I think that Sam is right that there are times when honesty does no one any good. It ought not be pursued as an end in itself but to serve us. After all we are there to serve the genes in a sense, and the genes make good for us (stochastically) what is good for them. For instance self preservation.
So we ought not se morality as serving anything but ourselves. We are designed (or are an evolvong genetic projecttion advancing through filter of history) as ‘survuival machines’ (to borrow from Dawkins). Morality helps us survive even it it is not 100 % (it is stochastically useful, probably uselful, for example in Islamic health concern, but not so much in terrorism). People ought not to lie when their (or the group’s) interests are served by the truth. Then we will do our job as costodians over our own welfare, over the value if life. This is an adaoptation (life having a value/s) and morality (thou shalt ....etc) is a cultural adaptation to the former basic adaptation of life value.