Voltaire, Treatise on Tolerance

The Calas affair(a judicial error in which a Protestant merchant from Toulouse was the victime in 1762) is best known for the vigorous intervention by Voltaire, who took a close interest in the affair and published his Treatise on Tolerance, on this subject, in 1763. It is a short text in which he denounces the misdeeds of the judges in Toulouse and makes a strong plea for tolerance, in his eyes the only protection from religious violence. In this extract, Voltaire wants to base human rights on natural rights (which are alone common to all) and, like Castellion two centuries before, invokes the golden rule. In the penultimate section of this extract, which covers great civilisations of the East and the West, he shows that intolerance is bound to end in pointless massacres.
Natural law is the law indicated to all men by nature. You have reared your child; he owes you respect as his father, gratitude as his benefactor. You have a right to the products of the soil that you have cultivated with your own hands. You have given or received a promise; it ought to be kept.
Human law must in every case be based on this natural law; and all over the earth the great principle—the universal principle of both—is: Do not do ·to others· what you would not want to be done to you. Now, I don’t see how a man guided by this principle could say to another: Believe what I believe—which you cannot believe—or you will perish, which is what men say in Portugal, Spain and Goa. In some other countries they are now content to say: Believe, or I detest you; believe, or I will do you all the harm I can; monster, you don’t share my religion so you have no religion; you should be a thing of horror to your neighbours, your city, your province.
If it were a matter of natural law to behave like that, the Japanese should detest the Chinese, who would abhor the Siamese; the Siamese in turn would persecute the Tibetans, who would fall upon the Indians; a Mogul would tear out the heart of the first Malabarian he met; the Malabarian could slaughter the Persian, who could massacre the Turk; and all together would fling themselves against the Christians, who have so long devoured each other.
So the ‘law of intolerance’ is absurd and barbaric; it is the law of tigers; except that it is even more horrible, because tigers tear and mangle only so as to have food, whereas we wipe each other out over paragraphs.