Robert A. Heinlein said this quote

“ For the first time in my life, I was reading things which had not been approved by the Prophet's censors, and the impact on my mind was devastating. Sometimes I would glance over my shoulder to see who was watching me, frightened in spite of myself. I began to sense faintly that secrecy is the keystone of all tyranny. Not force, but secrecy...censorship. When any government, or any church for that matter, undertakes to say to it's subjects, This you may not read, this you must not see, this you are forbidden to know, the end result is tyranny and oppression, no matter how holy the motives. Mighty little force is needed to control a man whose mind has been hoodwinked, contrariwise, no amount of force can control a free man, a man whose mind is free. No, not the rack, not fission bombs, not anything---you can't conquer a free man; the most you can do is kill him. ”