Multiplicity and opposition

Analyzing Plato’s critique of poetry, Schindler ( Plato’s Critique of Impure Reason: On Goodness and Truth in the Republic , 295) notes that the critique in the last book of the Republic is “not in the first place a moral one . . . but primarily ontological.” Schindler elaborates: “Wholeness has been a fundamental theme in the Republic from the very beginning . . . , and that this is the case because of the essential link between goodness and integrity. Such a view of goodness compels a question regarding the nature of multiplicity. To the extent that multiplicity presents itself in abstraction from a unifying order, the differentiation it implies cannot help but reduce to the mutual exclusion of parts. Multiplicity entails relative opposition, and if there is nothing but the relative, there is nothing but opposition.”

But why should multiplicity involve opposition, or differentiation imply exclusion? Why not relative harmony? Why an implicit ontological violence?