Reasoning, or logic, follows certain, non-arbitrary rules which must be adhered to if we wish to reach valid conclusions. These rules include non-contradictory identification and grouping by essentials. By applying the rules of logic consistently, we can hope to achieve objectively valid knowledge about reality. If we wish to survive we must act in certain ways. Moral behavior is that which tends to promote our survival.
Immoral behavior is that which tends to promote our destruction.
Where survival is not at issue, moral behavior will tend to promote security and happiness, immoral behavior insecurity and unhappiness. There are different levels of value. The higher values are those which make the lesser values possible. At the higher levels of value there is a community of interests among all rational, civilized human beings. The question of self versus others is irrelevant, in that one's self-interest and the interests of others are in fundamental harmony.