Plato's the Republic: Is Justice of Wisdom?

Plato has proved in the Republic that justice is not the interest of the stronger, the morality of the ruler, or the advantageous, but rather that justice is acting in one's own sphere and refraining from interfering in another's sphere. This definition works only in the context of Plato's republic wherein the idea of injustice, being the opposite of justice and not defined otherwise, has no place in the minds of the citizens. This kind of justice is not wisdom, but rather a kind of stagnation. Plato set out to mold a society made on the principles of justice only and not mutual advancement. The goal of Plato's society cannot be advancement because their is no understanding of gaining more than what is needed at any time. The principle of utilitarian placement of labor in society, a need of only subsistence, can only work if a society collectively buys in to that principle. Plato's society is not based on a want to destroy injustice in an already created one, but rather to create a society in which none of the citizens understand anything but their sphere.
Is this kind of society just in itself? Is it fair to deny the pursuit of knowledge and evolution to an entire populace? I don't believe it is and I don't believe it can work. I don't believe that injustice or justice are learned behavior. Humans have evolved through trial and error and the understanding of advantages. A society which contains merchants and exchange of goods and money affords opportunities for advantage to be found in these exchanges. The argument against this flaw is that the citizens of the republic will have no conception of unfairness or unfair dealings in exchange of goods. The will to be greater than others is an evolutionary maxim and cannot be taken out of a society.
And if it was, for argument's sake, is that just or good for the people of the republic? This principle denies any kind of evolution of man. The republic also does not exist isolated in the world. It will inevitably be a weak republic unless its citizens understand power. The warrior class of the republic would have to understand death and the search for a way in which to cheat death would open up avenues for injustice to creep in.
The denial of such supposed learned behaviors is not wise. It does not encourage a wise populace and it is unwise in itself. If a republic came to being such that it abided by the principle of subsistence as the only goal and everything remaining in its right place and still had an understanding of death as natural then Plato's republic could work. As it stands, Plato's just republic is unwise.