Socrates argues that there are actually 3 levels, or a vision of society that is tiered. What is an objection to that?
From the most fundamental of points of view, a critic of Socrates is that he fails to integrate the multiplicity and variance that is in the modern setting. The entire notion of the form is the belief in the singular notion of the good. In the Socratic world, there is one form, one singular and monolithic notion of what is good that should animate all reality. In much the same way, the construction of three levels in society fails to take into account the variance and difference that is present in the modern condition. In the desire to fit into this prescribed understanding of the good, varainces of individual voice and experience is silenced for this larger configuration. I think that this becomes a significant problem with the Platonic notion of justice and construction of society in his work. I tend to think that this comes down to a basic premise about whether or not one thinks that transcendence and harmony can be achieved from a political or civic point of view. I tend to think that there has been enough damage done in the name of and pursuit of the singular notion of the good. The construction of "higher" and "lower" levels of society and of human beings have led to some of the worst in human actions. While laying out his vision, consider in Book V the Platonic embrace of eugenics as part of this. Such an idea has been used to do some of the worst to social orders. While this is probably not Plato's or Socratic intent, I think that the singular notion of the good, the idea that there is one configuration to encompass all of society and human interaction, does more to silence voices than to enhance them. In this, I believe a valid argument against what is being advocated in Plato's work emerges.