I disagree that it requires a posconventional level of moral development. People strongly lean to match and reflect behaviors of others rather than invent their own, which is shown by various experiments. Defecting is a rational strategy, but we're irrational beings first (or rather überrational, with the same flavor as in "supernatural"). And our ethics emerges from our aesthetical principles, rather than on our intellectual decisions, because it's intimately tied to subjective experience of suffering. Aesthetics, in return, is largely shaped by familiarity. So, I think it's not a problem of "uplifting humanity to moral heights", but rather a question of normalizing cooperation in a society. After all, monkey see – monkey do.

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