In this paper, I defined deducing educational purposes based on an ideal society that was conceived arbitrarily by philosophical speculation as ‘Dogmatic Setting of Educational Purposes’. I analyze Plato's political and educational ideas, which is a representative example of the dogma. In Politeia, the idea of a republic cannot be reasonably explained due to ‘kallipolis-eidos paradox’ which means incompatibility with the idea of a republic and his theory of forms. Therefore the education that Plato has offered to bridge these gaps has degenerated into propaganda. Meanwhile, in Nomoi, Plato had overcome the ‘kallipolis-eidos paradox’ by modifying his theory of forms. However, since the law is based on Plato's own arbitrary legislation, education that forces citizens to voluntarily obey the law is nothing more than domestication. These consequences are inevitable as long as Plato maintain the ‘Dogmaic Setting of Educational Purposes’. In addition, these risks are inherent in the current branch of educational philosophy, as well as in Plato’s. Therefore, the philosophers of education are required to criticize the limitations of the philosophy of education.