Why 'should' atheists be moral?

[Angrboda]

Empathy may play a part in our morality, such as in deciding whether killing animals for food is right or not, but I don't think it's the whole story. I think the long and short of it is that when we contemplate something immoral, we have a gut level reaction of feeling negatively about that action, even before empathy kicks in. Empathy, rule of law, cooperation and so forth may be good justifications for being moral, but I think they come after the fact. The reason why we don't behave immorally is because we would feel anxious, uncomfortable and guilty for doing so. In some cases, too, it's just a conditioned response. We don't decide whether or not to run a stop sign at each stop sign we approach; it's just easier going along with doing the right thing to do. So we behave morally because it would be more difficult to function, psychologically, if we didn't behave morally. But morals can be culture specific. Mobsters and hit men may function just fine being constantly immoral. But not the rest of us. Still, we do fight that feeling occasionally. If you've ever pulled up to a stop light late at night, and the stop light doesn't change, we eventually pull through the red light. Even though we know it's okay in that instance to do so, many of us will still feel very uncomfortable doing so. So the long and short of it is that there is no ultimate reason why we "should" - we behave morally because it's in our nature to do so; it's what a healthy brain does. That may not be the sort of pragmatism which would satisfy the theist's question, but ultimately I think that's the explanation. We behave morally because we would feel uncomfortable in a special way if we didn't, and we're built to naturally avoid committing acts which raise that feeling in us.