Laudator Temporis Acti

Xenophon, Hellenica 2.3.29 (Critias speaking about Theramenes, 404 BC; tr. Carleton L. Brownson):

Therefore he ought to be punished, not merely as an enemy, but also as a traitor both to you and to ourselves. And treason is a far more dreadful thing than war, inasmuch as it is harder to take precaution against the hidden than against the open danger, and a far more hateful thing, inasmuch as men make peace with enemies and become their trustful friends again, but if they catch a man playing the traitor, they never in any case make peace with that man or trust him thereafter.

ὥστε οὐ μόνον ὡς ἐχθρῷ αὐτῷ προσήκει ἀλλὰ καὶ ὡς προδότῃ ὑμῶν τε καὶ ἡμῶν διδόναι τὴν δίκην. καίτοι τοσούτῳ μὲν δεινότερον προδοσία πολέμου, ὅσῳ χαλεπώτερον φυλάξασθαι τὸ ἀφανὲς τοῦ φανεροῦ, τοσούτῳ δ᾿ ἔχθιον, ὅσῳ πολεμίοις μὲν ἅνθρωποι καὶ σπένδονται καὶ αὖθις πιστοὶ γίγνονται, ὃν δ᾿ ἂν προδιδόντα λαμβάνωσι, τούτῳ οὔτε ἐσπείσατο πώποτε οὐδεὶς οὔτ᾿ ἐπίστευσε τοῦ λοιποῦ.