Book 3 and the "City"

In book 3 Socrates gets down to the means of the discussion of the just city. We see the whole exploration with the Guardians. In Book 2 Socrates told us that the education in this just city that he created must be of moral education. Basically I think he says here that there are only certain subject to which can be looked at and those that need to be put aside or ignored. We saw that in book 3 also when Socrates was trying to tell us that we should only tell the Guardians the good things and let them learn only good and not to associate with the bad. As said in class I don't like how this sounds. I have a suggestion of what should happen though. I think that Socrates should raise these Guardians as children in any way he wants. If that is knowing only the good then that is fine, but as they grow they should be exposed to everything which is even the bad and by the age of understanding and talking on the role of being Guardians then the once children should be able to decide and choose what they want for themselves. At the end of Book 3 the guardians lifestyle is more closely examined and it seems to be joyless. Socrates wants us to have these Guardians for the city because people were already unhappy with life if that is how I understand it. If the whole point of the Republic is justice, then is it even just to have Guardians? I hope someone can help me answer this question. I find this question hard to find an answer to. I want to believe that if it was truly a just city then there would be no need for Guardians, but I also think that to be just we might need that role model type person like the Guardians to help give us a push in the right position. If anyone wants to help me answer this question please do.