Thrasymachus is now out of the dialogue, having gracelessly told Socrates that Socrates was all along seeking to do Thrasymachus personal injury in making him look bad in the argument and that Socrates probably cheated somehow in achieving the final rebuttal. But Glaucon and Adeimantus want the conversation extended, Glaucon because he would like to accept Socrates' argument that justice is better than injustice, but he is not yet convinced; Adeimantus because he is troubled by the efficacy of the appearance of virtue as opposed to the possession of virtue in and of itself. Adeimantus is also troubled by other aspects he wants introduced in the dialogue. In other words, Glaucon wishes to hear Socrates amplify his rebuttal of Thrasymachus, so Glaucon will recapitulate Thrasymachus' arguments. And Adeimantus intends to break new ground in the conversation.
Socrates has said that Justice is a good, a virtue, not unlike good health and forms of human knowledge that are good in and of themselves. The attainment of the good is not consequent on the rewards (money, honor, prestige) it might entail.
But Glaucon's recapitulation of Thrasymachus' argument is of value, if only because it eschews the Sophist's bombast. Here it follows:
In the old days, there was no concept of justice, no laws to fix the locus of justice. People took by force of arms whatever they could from one another, but no group of people could ally themselves in sufficient force or philosophical consensus to assure their position of power. So they were unhappy because everyone was effecting retribution of evil upon others who had instigated the use of force, violence for violence, blood feuds, the wrongs of fathers visited upon sons. So people agreed to a sort of rude law, tried to establish "right" actions and "wrong" actions. But their laws were engendered by fear and motivated by selfish ends.
