Voltaire
Natural religion has a thousand times prevented citizens from committing crimes. A well-trained mind has not the inclination for it: a tender one is alarmed at it, representing to itself a just and avenging God; but artificial religion encourages all cruelties which are exercised by troops -- conspiracies, seditions, pillages, ambuscades, surprises of towns, robberies, and murder. Each marches gaily to crime, under the banner of his saint.

A certain number of orators are everywhere paid to celebrate these murderous days; some are dressed in a long black close coat, with a short cloak; others have a shirt above a gown, some wear two variegated stuff streamers over their shirts. All of them speak for a long time, and quote that which was done of old in Palestine, as applicable to a combat in Veteravia.

The rest of the year these people declaim against vices. They prove, in three points and by antitheses, that ladies who lay a little carmine upon their cheeks, will be the eternal objects of the eternal vengeances of the Eternal; that Polyeuctus and Athalia are works of the demon; that a man who, for two hundred crowns a day, causes his table to be furnished with fresh sea fish during Lent, infallibly works his salvation; and that a poor man who eats two sous and a half worth of mutton, will go forever to all the devils.

Of five or six thousand declamations of this kind, there are three or four at most, composed by a Gaul named Massillon, which an honest man may read without disgust: but in all these discourses, you will scarcely find two in which the orator dares to say a word against the scourge and crime of war, which contains all other scourges and crimes. The unfortunate orators speak incessantly against love, which is the only consolation of mankind, and the only mode of making amends for it; they say nothing of the abominable efforts which we make to destroy it.

You have made a very bad sermon on impurity -- oh, Bourdaloue! -- but none on these murders, varied in so many ways: on these rapines and robberies: on this universal rage which devours the world. All the united vices of all ages and places will never equal the evils produced by a single campaign.

Miserable physicians of souls! you exclaim, for five quarters of an hour, on some pricks of a pin, and say nothing on the malady which tears us into a thousand pieces! Philosophers! moralists! burn all your books. While the caprice of a few men makes that part of mankind consecrated to heroism, to murder loyally millions of our brethren, can there be anything more horrible throughout nature?

What becomes of, and what signifies to me, humanity, beneficence, modesty, temperance, mildness, wisdom, and piety, while half a pound of lead, sent from the distance of a hundred steps, pierces my body, and I die at twenty years of age, in inexpressible torments, in the midst of five or- six thousand dying men, while my eyes which open for the last time, see the town in which I was born destroyed by fire and sword, and the last sounds which reach my ears are the cries of women and children expiring under the ruins, all for the pretended interests of a man whom I know not?

What is worse, war is an inevitable scourge. If we take notice, all men have worshipped Mars. Sabaoth, among the Jews, signifies the god of arms; but Minerva, in Homer, calls Mars a furious, mad, and infernal god.

The celebrated Montesquieu, who was called humane, has said, however, that it is just to bear fire and sword against our neighbors, when we fear that they are doing too well. If this is the spirit of laws, it is also that of Borgia and of Machiavelli. If unfortunately he says true, we must write against this truth, though it may be proved by facts.

This is what Montesquieu says. "Between societies, the right of natural defence sometimes induces the necessity of attacking, when one people sees that a longer peace puts another in a situation, to destroy it, and that attack at the given moment is the only way of preventing this destruction.

How can attack in peace be the only means of preventing this destruction? You must be sure that this neighbor will destroy you, if he become powerful. To be sure of it, he must already have made preparations for your overthrow. In this case, it is he who commences the war; it is not you: your supposition is false and contradictory.

If ever war is evidently unjust, it is that which you propose: it is going to kill your neighbor, who does not attack you, lest he should ever be in a state to do so. To hazard the ruin of your country, in the hope of ruining without reason that of another, is assuredly neither honest nor useful, for we are never sure or success, as you well know.

If your neighbor becomes too powerful during peace, what prevents you from rendering yourself equally powerful? If he has made alliances, make them on your side. If, having fewer monks, he has more soldiers and manufacturers, imitate him in this wise economy. If he employs his sailors better, employ yours in the same manner: all that is very just.

From Voltaire, Philosophical Dictionary, in Works, A Contemporary Edition, Vol VII.