Why does Lewis Thomas express concern about what we would say to beings from another planet?

Lewis Thomas expresses concern about what we would say to beings from another planet because he believes our communication would reveal more about us than them. He suggests that our statements might unintentionally expose human folly, conflict, or shortcomings, which could create an unfavorable impression of humanity. Thomas emphasizes the importance of careful consideration and diplomacy in our interactions with extraterrestrial beings.