The doctrine of toleration requires a positive as well as a negative statement. It is not only wrong to burn a man on account of his creed, but it is right to encourage the open avowal and defence of every opinion sincerely maintained. Every man who says frankly and fully what he thinks is so far doing a public service. We should be grateful to him for attacking most unsparingly our most cherished opinions.

Leslie Stephen, ‘The Suppression of Poisonous Opinions’, The Nineteenth Century, vol. 13, no. 73 (April, 1883), p. 665