"Free speech, may indeed best serve its high purpose when it induces a condition of unrest, creates dissatisfaction with conditions as they are or even stirs people to anger." - Justice Douglas
The above quote by Justice Douglas came from the case Terminiello v. City of Chicago (1949)
Another of his interesting quotes:
"Inanimate objects are sometimes parties in litigation. A ship has a legal personality, a fiction found useful for maritime purposes. The corporation sole - a creature of ecclesiastical law - is an acceptable adversary and large fortunes ride on its cases.... So it should be as respects valleys, alpine meadows, rivers, lakes, estuaries, beaches, ridges, groves of trees, swampland, or even air that feels the destructive pressures of modern technology and modern life. The river, for example, is the living symbol of all the life it sustains or nourishes - fish, aquatic insects, water ouzels, otter, fisher, deer, elk, bear, and all other animals, including man, who are dependent on it or who enjoy it for its sight, its sound, or its life. The river as plaintiff speaks for the ecological unit of life that is part of it."
I came across his free speech quote in this article in the New York Times: Images, the Law and War.