My opinion...

Self-interest is a primordial instinct needed for survival amongs all species not only humans.
First comes self-interest then group-interest. This is not only for survival, but also a means of natural selection as a species evolves and grow stronger.

Competion is at the base of both self and group interest to strengthen the process of natural selection and thus creating a stronger species through evolution ie. two males in the same group will have a competition of some sort in order to gain the favour of a female and then produce offspring and those same two males will then fight side by side should they compete for survival against another group of the same species. The winner takes it all.

This means self-interest, group-interest and competion is part of our natural instincts to ensure the species grow stronger and survive.

It is selfishness that will cause an individual or group to resort to inappropriate behavior, like cheating, stealing or lying, especially in humans, to gain an unfair advantage, which undermines the concept of natural selection.

This will eventualy be the cause of weakness in the evolution of the whole species, should it be left unchecked.

Great article!