[Copernicus]

"And again, if most men agree with "your" principle, whether on a transactional or moral basis, doesn't that indicate such a principle, at some minimal level, is inherent in man? How can it be otherwise? "

Nothing is "inherent in man". Mankind has learned through time how best to manage interrelationships, and those learnings vary from society to society and are passed down/evolve within that society. Man is an animal that happens to have evolved beyond the capabilities of other animals, thats it. Lower animals learn how to best deal with interrelationships and form societies as well.

The "golden rule" is one societal framework for interrelationships. It is of course, a utopian framework that is woefully incomplete unless it is universal. Since it isn't universal there needs to be at least one more rule, such as "but if my neighbor will not treat me in that way, then I sure as hell better mistreat him first".