> anyone who deliberately did less than her ability
> allowed would soon become a social outcast
A sadistic will to power may not characterize all political and other social relations, but it certainly characterizes some, and some much more than others. Moralistic conceptions of ethics are one of its common hiding places.
The rational reason for contributing in accordance with your ability is that it's in your "interest" to do so where your interest is the rational one of living a fully good life.
Punitive (most likely also retributive) treatment is inappropriate if this is true and if the circumstances required for the development of the "powers" required to live such a life are inconsistent with such treatment.
A society in which a willingness to impose it was widespread would be far from ideal.
Look, for instance, at the kind of government that results from successful demagogic appeals to punitive, retributive attitudes to welfare and crime.
Ted