It sounds to me like you're reporting a muddled version of the Melian Debate in Thucydides, but there are details you state that make this identification difficult. "Hellenistic" is not a synonym for "Greek," it refers to the expansion of the Greek speaking world into formally Persian-held areas and the total transfer of political prominence from mainland Greeks to Macedonians. The Hellenistic Period is traditionally dated as beginning at the death of Alexander, by which time the Melian Debate and the Athenian Empire were ancient history, with Athens reduced largely to an intellectual center with little political importance. If you're really talking about the Hellenistic Period I have no idea what you're talking about. What you describe is not what Thucydides says, but I can see how you might have gotten there, if we're both talking about the Melian Debate. Melos was a neutral city in the Peloponnesian War, but it was ethnically Dorian and the Athenians demanded it pay tribute in 416. When the Melians refused the Athenians laid siege to the city and sacked it. Thucydides inserts a series of dialogues between the Athenian envoys and the Melian magistrates, which serves as a counterpoint to his earlier Mytilinean Debate (which I suppose you might also be talking about, but the result is different). Thucydides has the Athenians in Book 5 say that the Melians can either surrender or be wiped out. They deliver the famous line (5.89), which I think you're misremembering, "δυνατὰ δὲ οἱ προύχοντες πράσσουσι καὶ οἱ ἀσθενεῖς ξυγχωροῦσιν," "those possessed of power cause to pass [what they wish] and the weak yield." Thucydides has the Melians reply that Athens has no right to attack a neutral city, to which the Athenians react that Melos' relationship with the Spartans is a threat and that if the Melians are not made a tributary the Athenians will look like they were unable to expand and control the empire. The dialogue goes on like this, with the Athenians repeatedly appealing to the Melians' sense of pragmatism and the Melians countering with moralist arguments. But the Athenians do not accede the superiority of the Melian position as you say, they end negotiations because it's clear that the Melians refuse to think practically and will insist on fighting a doomed defense. This is in contrast with the Mytilinean Debate, in which the Athenians decide the next day to overturn Cleon's motion to massacre the city on the grounds that it would be unjust. The Melian Debate in Thucydides is inserted (it seems highly unlikely that any debate that took place looked quite like the manufactured philosophical dialogue Thucydides inserts in Book 5) as a counter to the Mytilinean Debate. Whereas, Thucydides says, the Athenians remained true to their senses of morality and justice in the face of the Mytilinean revolt, the war and the empire had so corrupted them by 416 that the Melian invasion was handled completely differently