That is, indeed, a scaling up. And yes, close communities of friends do indeed exist.
See. The idea when I say scale it up to a reasonably sized society and to scale it up to a reasonably sized society. A group of friends is in no way reasonably sized. It is not scaled up from a family. And I am not saying that they do not exist, but rather that there is no one way they are held together.
A city where everyone's ideal is to "do what they owe" will function perfectly. The question is one of surrounding culture.
This right here is the crux of what I was trying get to here. How do you expect such a society to exist without any form of force?
Brainwashing, indoctrination, pharmaceuticals, eugenics. All of these might be used to give rise to a society like that, but none of them can be considered anything other then force. Such a culture is both unstable and to a degree unnatural.
Assuming a society, an aggregate of individuals--that is, people functioning separately, thinking only of themselves, no matter how power is applied to force them to act for the sake of others--is doomed to failure a priori.
Tautological Latin aside, I question why this is. Of course a society like that would have a hard time forming, but once formed I don't see the issue with it. The basic assumption here seems to be that their would be constant rebellion against the force that is making them help other. But by your own words they are only thinking of themselves, so such a rebellion would only happen when the consequences of such a action would be less then the consequences of not taking the action. IE: If one was required to pay 5% of ones income to help the poor one would still pay that and not rebel if the cost of rebelling was more then 5% of ones income.