Gorgias (No, Not Georgia)

My first tentative reconnoiter into the field of Greek literature after reading Who Killed Homer, was with the playwright Aeschylus. While all went well, I did not learn much, and subsequently, have nothing to report. But though my first foray was unfruitful, the adventure I am currently in the middle of has already yielded a wealth of interesting things. I am, as it were, still on the front lines, in that I have not yet finished exploring Plato's Gorgias. I only have a partial picture of Socrates' dialogue (did the spelling change to dialog recently and I missed it? Spell check isn't happy with me and I'm not happy with it.) with Gorgias and Callicles on the purpose of oratory.

Even though I started with the intent to learn what Plato thought about public speaking because I am enrolled in a public speaking class, my interest has been taken captive by the discussion of good and evil that he creates. Basically, Plato, speaking through Socrates, claims that the evil man who inflicts harm is more miserable than the good man who unjustly receives it. Also, the wrongdoer who escapes harm is more miserable than the wrongdoer brought to justice.

Even if, like Callicles, we disagree with what Plato says about a disciplined and upright life being a happier state to live in than unrestrained immorality, where does the differentiation between good and evil come from? In other words, why does Plato (a pre-christian) even recognize the existence of good and evil, right and wrong? And further, see the two alternatives as the most important choice a person can make?

O.k. I want to read a few more pages of this dialogue (or dialog) before bed.