Plato, Laws 819a

φοβοῦμαι μὲν καὶ ταῦτα ἃ σὺ νῦν λέγεις, μᾶλλον δʼ ἔτι δέδοικα τοὺς ἡμμένους μὲν αὐτῶν τούτων τῶν μαθημάτων, κακῶς δʼ ἡμμένους. οὐδαμοῦ γὰρ δεινὸν οὐδὲ σφοδρὸν ἀπειρία τῶν πάντων οὐδὲ μέγιστον κακόν, ἀλλʼ ἡ πολυπειρία καὶ πολυμαθία μετὰ κακῆς ἀγωγῆς γίγνεται πολὺ τούτων μείζων ζημία. ἀληθῆ λέγεις. τοσάδε τοίνυν ἑκάστων χρὴ φάναι μανθάνειν δεῖν

I am indeed scared about the habit you mention, but I am still more alarmed about the people who take up these very sciences for study, and do so badly. Complete and absolute ignorance of them is never alarming, nor is it a very great evil; much more mischievous is a wide variety of knowledge and learning combined with bad training. That is true. One ought to declare, then, that the freeborn children should learn as much of these subjects as the innumerable crowd of children in Egypt learn along with their letters.