I agree with you, and I strongly suspect I am not about to say anything that you haven’t said, but just to clarify - the possession of that value system in an environment that renders that value system successful is the key. We seem to have achieved an equilibrium with respect to the individual and the environment (at least, as far as I know, in much of the world) in which a “do not markedly and obviously harm others” value system is supported, and people can perceive themselves as successful within the confines of that system.
I think a clear argument can be made, however, that there are a set of circumstances that will make any “nice person” indistinguishable from a “selfish asshole.” No doubt there are countless examples, but having just seen “The Magdalene Sisters,” it is fresh in my mind, and institutions putatively founded on principles of kindness and compassion can effect the most horrific of behaviors by individuals who nevertheless believe they are (and are seen by others as) “nice people.”
Were a drastic negative change to occur to our current sociopolitical environment in America, you would no doubt see a drastic change in people’s value systems, such that anything that helps me and my family will be acceptable. Yet, even as things are, we tend not to directly harm others, but I know that I have a nice big screen TV and a new sporty car, and my conscience is only slightly pricked when I see the conditions that others live in here in our country. It is salved enough when I write my charitable contribution checks and vote for Democrats and liberals. Contrary to what many here would say, I am a “nice person,” but how would anybody but a “selfish asshole” be okay with the inequalities I just noted?
I was thinking about this discussion on Friday while attending a lecture. The lecturer reminded me about studies of the voles. It turns out that two types of voles, the prairie voles and the mountain voles are, naturally, largely similar to one another. Yet one of them (I think it is the prairie vole) has developed socialization around pair-bonded mating, and the other is socially isolative. Thus, it isn’t inconceivable that humans have evolved in such a way that we are geared to greater socialization. There are also studies of individual differences in the development of empathic responses in infants and children.
I would say that an avoidance of killing other people is a complicated combination of evolutionary processes, innate predispositions and societal structures, and that logical constructions play very little part in all of this. Most killers can express a logical construction - highly idiosyncratic, of course - to justify their actions.