I certainly cannot provide anything approaching a good explanation, but I think that when 'a defense of the rightness of class society' has to be formulated in the face of discourse on and real threat of 'democracy' (necessarily limited as 'democracy' was, in that it was a democracy of 'free men' minus women, slaves, and foreigners), ingredients for individualism may materialize, such as ideas of meritocracy, of each and every citizen as foundations of the 'democratic' & imperial state's glory (which, in turn, allows each to take part in 'universal morality' [= abstract principles of justice] and 'immortality'), etc.
"But before I praise the dead, I should like to point out by what principles of action we rose to power, and under what institutions and through what manner of life our empire became great... Our form of government does not enter into rivalry with the institutions of others. Our government does not copy our neighbors', but is an example to them. It is true that we are called democracy, for the administration is in the hands of the many and not of the few. But while there exists equal justice to all and alike in their private disputes, the claim of excellence is also recognized; and when a citizen is in any way distinguished, he is preferred to the public service, not as a matter of privilege, but as the reward of merit. Neither is poverty an obstacle, but a man may benefit his country whatever the obscurity of his condition." (Thucydides, "Pericles' Funeral Oration")
What about Plato? It is telling that in _The Republic_, Plato has Socrates first vanguish Thrasymachus--a young Sophist who argues that justice is whatever the powerful decide it is and that the powerful decide whatever is in their best interest to be just--by stating that the powerful hardly know what is in their best interest (here a cunning substitution of an epistemic question for that of a political one.). And then only after the rhetorical defeat of Thrasymachus does Plato/Socrates truly begin an apology for class society. The rule by the 'best' (= aristos) cannot be made to sound plausible as long as rulers are portrayed as acting out of class-interest. By dispelling the specters of class-interest through an epistemic fallacy, Plato can now argue for abstract principles of virtue--unchanging products of reason beyond the visible world--that each citizen must embody in public political life, and only equally abstract ideas of individuals separated from social relations and selfish passions will in the end serve as plausible bearers of such first principles (thouogh in Plato's Republic, citizens are not quite separated from social relations, since they must at least fit into one of the three slots: guardians, auxiliaries, and producers).
Yoshie