I think you are over-optimistic about human goodness. If you had to deconvert at all it is possible you are from a culture where Christian morals still go strong amongst atheists. (Comparison: I do not remember any family members with a personal belief, I do remember some great-grandmas who went to church because it was a social expectation, but I think they never really felt entitled to form a personal belief or deny it, it was more obedience in observation than faith.) These kinds of habits don't die too quickly, in fact they can take centuries - there is the hypothesis that the individualism of capitalism came from the Protestant focus on individual salvation.

My point is that this "goodness" is probably more culturally focused than genetic. While it may be possible that if people are really careful they can keep it on and on within an atheistic culture forever, it can break down pretty easily. Christianity tends to push a certain universalism - without that, if no effort is made to stop it, things probably regress to the tribal level. We cannot really maintain universalism without effort - it can be an atheist effort, but it must be a very conscious one.

As my life experience is the opposite - to me religious faith is really exotic - it seems to me that the difference is that religious folks and perhaps post-religious atheists for a generation or two keep moral things real - talk about right and wrong as if it was something as tangible as money. But in my experience it washes out after a few generations and then only money, power, status stay as real things, because they receive social feedback but right and wrong doesn't.

To put it differently - religions form communities. Atheists often just hang out. So there is a tendency to form looser, not so tightly knit social interactions. In a tight community, right and wrong gets feedback, people judge each other. When interaction becomes looser, it is more like why give a damn what some random guy thinks about what I did t was right or wrong? But things like power, status, money still work even in loose interactions, so people become more machiavellian. At least that is my experience. I am not claiming this universalistic goodness cannot be maintained in atheistic cultures, I am just claiming it requires a special, conscious effort, it does not flow from human nature.

I also think you typically get this "goodness" culture if you participate in a culture who thinks of themselves as high-status winners, on an international comparison. Sharing is a way to show this status, this surplus. It requires a certain lack of bitterness. If you feel like your group was maltreated by greater powers, or invaders etc. you will probably stick to the group. Thus sharing still happens in less winner cultures but more on a personal level, family, friends, not with strangers.

This over-optimism about goodness is a typical feature of LW and the Rationality book, so I guess you will feel more at home here than I do. To me it comes accross as mistaking the culture of the US as human nature.

I have not formulated this exactly, but I think there is such a thing as a "winner bias". It is very easy for someone from the Silicon Valley to think the behaviors there are universal, precisely because being powerful and succesful gives on the "privilege" to ignore everything you don't like to see. The most extreme form is a dictator thinking everybody agrees because nobody dares not to, but it also exists in a moderate form, that the voices of more succesful people and cultures being louder, hence coming accross as more popular, more universal unless you know the alternatives first-hand. However they are pretty sure not universal - if they were the whole world would be as succesful as SV. Well, or at least closer.

For example, a typical "winner bias" may be reading interviews with succesful CEOs and thinking this is how all CEOs think. No - but the mediocre ones don't get interviewed. So it is more of an availability heuristic. The availability heuristic forms a winner bias making first-worlders think everybody thinks like first-worlders, because voices that are not propped up by success are not heard accross oceans. The other way around is not true, of course.

However I think this "winner bias" is more than just an availability heuristic. Probably it has also something to do with not having egos hurt from other groups having higher status.