I am a retired aerospace engineer with an interest in understanding morality as the product of biological and cultural evolution. I have a blog on this subject at moralitysrandomwalk.com. ,Seattle, USA
Increasing the benefits of cooperation is the primary reason morality exists in all cultures. This norm (plus punishment of violators) summarizes the most powerful cooperation strategy known - indirect reciprocity. So it summarizes morality, as Jesus wisely observed long ago.
Too severe internal punishment, by guilt and shame, reduces motivation to do anything, including good, and too severe external punishment provokes retaliation. Both are immoral because they contradict the function of morality, increasing cooperation.
The biology responsible for our experience of durable well-being was primarily selected for to reward cooperative association with family, friends, and larger groups. Therefore, moral behavior (cooperation in groups) is the most reliable way to increase durable well-being.
By exploiting efforts at cooperation you 1. motivate retaliation and ostracism by others, 2. reduce the benefits of long term cooperation, and 3. reduce your experience of durable well-being triggered by successful cooperation.
If everyone treated their own children equally to every other child, everyone’s efforts would be so diluted and inefficient as to reduce the benefits of cooperation – to be immoral. As John Rawls argued, we are obligated to treat people fairly, but not necessarily equally.
Swayed by our biological preferences for hedonistic short term rewards and in the heat of the moment of decision, we tend to make bad predictions of what will increase our durable well-being. In contrast, behaving morally is a much more reliable guide to increased well-being.