History of the Peloponnesian War

"Now consider what an error you would commit in this also, if persuaded by Cleon.

For at present the commons in all the states are well disposed towards you, and either do not revolt with the aristocratical party, or if compelled to do so, are straightway hostile to those who made them; and you have the mass of the city opposed to you on your side, when you proceed to war.

But if you butcher the commons of Mytilene, who took no part in the revolt, and when they had got possession of arms, voluntarily gave up the city; in the first place you will act unjustly by slaying your benefactors; and in the next you will produce for the higher classes of men a result which they most desire; for when they lead their cities to revolt, they will immediately have the commons on their side, because you had shown them beforehand that the same penalty is appointed for those who are guilty and those who are not.

On the contrary, even if they were guilty, you ought to pretend not to notice it; that the only class still allied with us may not become hostile to us.

And this I consider far more beneficial towards retaining our empire—that we should voluntarily be treated with injustice—than that with justice we should put to the sword those whom we ought not. And so the identity of the justice and expediency of the punishment, which Cleon asserts, is found impossible to exist therein.