The difference between true knowledge on a subject and the act of creating belief in the same subject are two different things. Plato prefers the first, being knowledge. True knowledge requires the actual experience of learning and having your own thoughts and opinions on it. Plato finds it hard to believe that an argument changing someone’s mind on justice for example is not very reliable. The argument Plato presents is that arguments that create justice where knowledge is absent can be dangerous. There is no way of knowing for sure what the truth is when there is rhetoric trying to convince a set of jurors on what to believe. Deceitfulness is very easy to get away with in these situations where you have people who have no knowledge being persuaded into believing something someone has said. Rhetoric in these kinds of situations within large audiences (aka “among the ignorant”) that don’t have knowledgeable people. Plato goes on to say that if you have your own knowledge about justice, you will be less likely to be taken advantage of. The real concern for Plato lies in his mistrust of the Sophists. He doesn’t believe that they even know justice, just creating belief for their side and leaving real justice falling by the waistside.
HR: Herrick, Plato, book