“The right to think, to know and to utter,” as John Milton said, is the dearest of all liberties. Without this right, there can be no liberty to any people; with it, there can be no slavery.

John A. Andrew (1818-1867) American lawyer, politician, abolitionist
Letter (1860)
    (Source)

Letter written after his election as Massachusetts governor. referencing Milton's Areopagitica. Quoted by Wendell Phillips in his "Mobs and Education" speech (16 Dec 1860), and often attributed to Phillips.