I think this argument is the one where the SDMB empirical rationalists (yes, I know I coined a new phrase) will find themselves running out of steam.
A few weeks ago people jumped all over me for asserting that there is such a thing as a soul. But I don’t think it is possible to establish a moral code without a spiritual component, albeit an informal one.
Operating purely out of self-interest isn’t the same as having a moral code - according to that logic there’s nothing to prevent one from being opportunistic, exploitive, manipulative and deceitful if one is confident of not being caught. Following the letter of the law rather than its intent, using fine print and misleading advertising to cheat people legally - these are fine examples of self-interest morality. How about exploiting children, the elderly and the mentally disabled? There was a time when it was pretty easy to get away with such things - why would that have changed, if it weren’t for a morality based on something more than self-interest?
And if it’s just all about self-interest, then how can a person ever be wrong? Caught, yes; but wrong, no.
I also don’t think it’s a simple matter of parental training & societal pressure - otherwise you wouldn’t have seen any abolitionists in the South. Or hippies from wealthy families.
I propose that human beings are hardwired with a soul that enables us to experience a sense of a larger reality, an energy of life - “the force”, if you will. And once we’ve gotten to know ourselves and our beliefs we can see beyond our immediate needs to a greater sense of “right” and “wrong”. That sense sometimes causes us to act against our immediate self-interest in order to achieve a larger goal of which we are a part. A belief in something more than our selves. It takes time and effort to develop such a sense, which is why the threat-of-Hell shortcut has been so often employed.
The fact that people attach a value meaning to certain altruistic acts (saving someone’s life, doing good without being recognized for it) and despise others is, to me anyway, clear evidence that a spiritual reality beyond self-interest is exerting an effect.
Anyway I don’t think the vast majority of people are operating purely out of self-interest. Otherwise the worst elements of the free market would be running rampant & no one would object to kiddie porn, torturing animals, or shooting paintballs at nekkid womens. We’re a lot more than just reasonable machines.