If you can't find utility in the concept of sin and evil, then I don't know how you can find utility in the concept of the good.
At Slate on evil, Neuroscientists suggest there is no such thing. Are they right? A quote:
Of course, people still commit innumerable bad actions, but the idea that people make conscious decisions to hurt or harm is no longer sustainable, say the new brain scientists. For one thing, there is no such thing as "free will" with which to decide to commit evil. (Like evil, free will is an antiquated concept for most.) Autonomous, conscious decision-making itself may well be an illusion. And thus intentional evil is impossible.
Many people do make conscious decisions to be hurtful or destructive. What could be more obvious? These neuroscientist folks can't see the mind for the neurons, it seems to me. As always in such cases, however, a conversation with the scientists would reveal that they do, themselves, lead lives in which good, evil, and choice are operative. Otherwise, they would deserve no recognition for their research because it was just their neurons making them do it.
Relevant good book: Columbia Prof Andrew Delbanco's The Death of Satan