Plutarch De capienda ex inimicis utilitate 6

[6] There may be, then, so much that is profitable and useful in reviling one’s enemy; but no less profit lies in the alternative of being reviled oneself and ill spoken of by one’s enemies. Hence Antisthenes ¹ was quite right in saying that, as a matter of self-preservation, men have need of true friends or else of ardent enemies; for the first by admonition, and the second by reviling, turn them from error. But since friendship’s voice has nowadays become thin and weak when it comes to frank speaking, while its flattery is voluble and its admonition mute, we have to depend upon our enemies to hear the truth. For as Telephus, ² unable to find a suitable physician, subjected his wound to his enemy’s spear, so those who are cut off from benevolent admonition must submit with patience to the remarks of a malevolent enemy if he exposes and reprehends their vice, and they must give consideration to the facts only, and not to what is in the mind of the detractor. Another parallel is the case of the man who, with intent to kill the Thessalian Prometheus, ³ smote with his sword a tumour which Prometheus had, and opened it so that the man’s life was saved, and he obtained relief from his tumour through its bursting; so oftentimes reviling launched upon a man by the prompting of anger or enmity cures some evil in his soul which either was not recognized or was disregarded by him. But most persons on being reviled do not stop to think whether the reproach is applicable to themselves, but they try to think what other form of reproach is applicable to the reviler, and, just as wrestlers do not wipe the dust from off their own bodies, so these persons do not wipe off the revilings from themselves, but they besmear one another, and in consequence get besmirched and begrimed by each other as they grapple together. But it is more imperative that the man who is ill spoken of by an enemy should rid himself of the attribute in question, than that he should get rid of a stain on his clothes to which his attention has been called; and if anybody mentions things which are not really attributes of ours, we should nevertheless seek to learn the cause which has given rise to such slanderous assertions, and we must exercise vigilance, for fear that we unwittingly commit some error either approximating or resembling the one mentioned. For example, an unwarranted suspicion of unmanliness was aroused against Lacydes, king of the Argives, by a certain arrangement of his hair and a mincing gait, and Pompey ⁴ suffered in the same way on account of his habit of scratching his head with one finger, although he was very far removed from effeminacy and licentiousness. Crassus ⁵ incurred the charge of being too intimate with one of the Vestal virgins, when he only wanted to buy from her a piece of good land, and for this reason had many private interviews with her and paid her much attention. Again, Postumia’s ⁶ ready laughter and overbold talk in men’s company put her under unjust suspicion, so that she was tried for unchastity. She was found innocent of the charge, but in dismissing her the Poritifex Maximus, Spurius Minucius, reminded her that the language she used should have no less dignity than her life. And again Pausanias inflicted on Themistocles, ⁷ who was doing nothing wrong, the suspicion of treason by treating him as a friend, and by writing and sending messages to him continually.