1.4-5 (tr. T.R. Glover):
For what could be more unjust than for men to hate a thing they do not know, even though it really deserves hatred? It can only deserve hatred when it is known whether it does deserve it. But so long as nothing at all is known of its deserts, how can you defend the justice of the hatred? That must be established, not on the bare fact of its existence, but on knowledge. When men hate a thing simply because they do not know the character of what they hate, what prevents it being of a nature that does not deserve hate at all?
Quid enim iniquius, quam ut oderint homines quod ignorant, etiam si res meretur odium? Tunc etenim meretur, cum cognoscitur an mereatur. Vacante autem meriti notitia, unde odii iustitia defenditur, quae non de eventu, sed de conscientia probanda est? Cum ergo propterea oderunt homines, quia ignorant quale sit quod oderunt, cur non liceat eiusmodi illud esse, quod non debeant odisse?
John E.B. Mayor in his commentary ad loc. cites Epistle to Diognetus
5.17 (here in Bart D. Ehrman's translation):
And those who hate them cannot explain the cause of their enmity.
καὶ τὴν αἰτίαν τῆς ἔχθρας εἰπεῖν οἱ μισοῦντες οὐκ ἔχουσιν.