Euripides, Bacchae 196

“We alone are right-minded; everyone else is wrong.”

μόνοι γὰρ εὖ φρονοῦμεν, οἱ δ᾽ ἄλλοι κακῶς.

Teiresias speaking to Cadmus; the sentiment, however, has achieved a universal currency among all members of humanity.