> People have a strong instinct for reciprocity and it is strongest when it is entirely their choice.

My experience disagree with that statement. The places where I find the strongest form of reciprocity is when social norms heavily emphasize reciprocity and punish defectors, which is typical in environments where peoples survivability depend on social norms and reciprocity.

A typical example is rural community vs a city. In a rural community there is existing and historical dependency on reciprocity to handle accidents (a barn burning down, a poor harvest, a bad hunt/fishing season, and so on). Defectors from the social norms can be punished for several generations ("I remember that your grandfather did not help my grandfather"), which makes defecting rare and expensive. The stereotypical example from large cities is that a person can bleed out on the street and people will continue to walk past, pretending to not see.

Naturally neither is an utopia and both has their own problem, but saying that the strongest form of reciprocity is found in places with no social norms, social expectations or enforcement seems to be plainly wrong from my experience.