If Athens had supported the helot rebellion like the Spartans feared, they would have suffered no additional negative consequences (the Spartans reacted as if the Athenians were intent to support the helots), Athens would have won the Peloponnesian War in advance by ethical means, and the unrivaled democratic empire would have been an uncompromised example to history.

Athens lost the Civil War the instant that it ceded its moral superiority over the slavers. This is how you produce Thucydides in a culture that was worthy of Pericles. This is how you become dominated by Philip II when your culture was worthy of being liberated by Socrates.