The just man then, as it seems, has come to light as a kind of robber, and I'm afraid you learned this from Homer. (334a)
Socrates is taking Homer to task for portraying the just man in a negative light. This is pretty early on in the dialogue, which just goes to show that Socrates is up in arms about poetry and its portrayal of justice from the get-go.
Then for many, Polemarchus—all human beings who make mistakes—it will turn out that to be just to harm friends, for their friends are bad and just to help enemies, for they are good. So we shall say the very opposite of what we asserted Simonides means. (334d-e)
As Socrates and his pals try to make sense of this slippery term "just," Socrates, in his typical way, shows how nothing is ever simple: since people constantly make mistakes, Socrates points out that we can't rely on most people's judgment to make sense of concepts like "good," "bad," and "just."
"But as to what each [justice and injustice] does with its own power when it is in the soul of a man who possesses it and is not noticed by gods and men, no one has ever, in poetry or prose, adequately developed the argument that the one is the greatest of evils a soul can have in it, and justice the greatest good." (366e)
Socrates is laying out his agenda here. He wants to show how beneficial and great justice can be for an individual person, regardless of whether anyone, human or divine, notices that this individual is just. Philosophy to the rescue.
"Unless the philosophers rule as kings or those now called kings... adequately philosophize, and political power and philosophy coincide in the same place.... there is no rest from ills for the cities..." (473d)
Even though some people accuse philosophy of being a heady, impractical kind of discipline, Socrates is devoted to proving that philosophy is necessary for political power. (We're not surprised to hear that this means philosophers have some perks in Socrates's city.)
Won't we also then assert that the philosopher is a desirer of wisdom, not of one part and not another, but all of it?" (475b)
Socrates makes it clear that there are no short cuts or half measures for a true philosopher seeking wisdom. It's a full-time job, and it's serious business.
"But by far the greatest and most powerful slander comes to philosophy from those who claim to practice such things." (489d)
Even Socrates admits that it's sometimes philosophers themselves who give philosophy a bad rap. For Socrates, being a real philosopher means that you will behave in a way informed by philosophy. There are a lot of duds out there saying they're philosophers and acting in stupid ways, thereby giving philosophy a bad name.
"What is most surprising of all to hear is that each one of the elements we praised in [the philosophical] nature has a part in destroying the soul that has them and tearing it away from philosophy." (491b)
With great power comes great responsibility, right? Sounds like philosophers and superheroes have some things in common. The kind of people who are capable of becoming philosophers have such a special and unique blend of qualities that if just one little thing goes wrong, those special qualities can unite for evil. Yikes.
"Then it's impossible... that a multitude be philosophic...and so those who do philosophize are necessarily blamed by [the many]." (494a)
Socrates doesn't have much good to say about crowds and multitudes. In fact, any time you see the phrase "the many" come up in Plato, you can be pretty darn confident that nothing nice is coming after. The reason for this is likely that both Socrates and Plato value each individual's critical thought, self-examination, and skepticism. Critical thought, self-examination, and skepticism are not qualities you find in crowds of people.
"...but this is the very charge I'm bringing; not one city today is in a condition worthy of the philosophic nature." (497b)
Too bad the imaginary city Socrates and his friends have spent all this time forming isn't real, because Socrates believes that there isn't anywhere even remotely close to channeling the benefits of philosophy. How does the republic sound to you? Would you want to live there? Why or why not?