Plato 's defense of justice in the « Republic » is flawed.
His aim is to show that justice pays.
To prove this, he must show that just action pays the just agent ; in order to show this he must demonstrate that just behavior is good in itself.
But a requirement for the government of the ideal city is that the philosopher-kings regard ruling as an intrinsic evil (520 D-521 B). In this case, Plato 's argument that justice is in one 's self-interest breaks down.
Plato faces another serious problem that has not been recognized : for almost all members of Plato 's ideal polis, when justice is a matter of doing one 's job, justice does not pay.
The greater intrinsic evil of lower forms of work establishes that those forms of work are not in the self-interest of the producers (346 D 6-8 ; 347 A 1-2 ; 495 D-E).
