Let but the public mind become once thoroughly corrupt, and all attempts to secure property, liberty or life, by mere force of laws written on parchment, will be as vain as to put up printed notices in an orchard to keep off the canker-worms.
Source, in full
p. 214; sometimes paraphrased as: "Let the public mind become corrupt, and all efforts to secure property, liberty, or life by the force of laws written on paper will be as vain as putting up a sign in an apple orchard to exclude canker worms."