Interview with "The most dangerous man in America", whistleblower Daniel Ellsberg
A short excerpt from this interview where Daniel Ellsberg answers to the question "How security clearance changes a person?":
First reaction will be amazement that all this information existed and you'll feel like a fool that you didn't know about it before... {...}
But after a little while you get used to it and you feel that everyone else who doesn't have the clearances is a fool and you'll find that you'll be speaking to people and saying "what would they be telling me if they knew what I knew?" which by the way {...} might be true or false {...} it was just highly secret it didn't have to be true.
"What would they do?" well that's too complicated so you'll stop listening and all you'll be doing is you won't learn from anyone you'll just think of what you want to tell them what you want them to believe you'll become something like Circe's captives in the Odyssey who had a potion that turned men into swine they couldn't communicate like men anymore.
He explains how difficult it is to take people without clearance seriously.
IMHO this is remarkably similar to situation when one has to argue against established policy.
My conclusion: secrecy poisons communication between people.
Daniel Ellsberg is my hero.