Socrates and Virtue

Socrates, for one, was fairly cheerful about being put to death unjustly. But does socrates have an argument for this attitude, or does he just want to lead by example? And here it is. He gets polus to agree that justice is a good thing and injustice a bad thing. Things are good either because they are pleasant, or because they are beneficial, or both. With unjust things, it will be the opposite. Since they're bad, they must be either unpleasant or harmful - or both. People who lack virtue are those who don't know what is good for them.