“When Voltaire was bornreally but one church which, of course, was ignorant, tyrannical and barbarous in the extreme. All creeds are alike, and whenever there is but one, and the rulers honestly believe in that one, they are bound to be ignorant, barbarous and cruel. All sorts of heresies were punishable by death. If anyone dared to write a pamphlet or book that questioned any part of the accepted faith, the book was at once consigned to flames and the author was lucky if he did not meet the same fate. Religion was not maintained by the precepts of the priest, but by the prison, the torture chamber and the fagot. Everyone believed; no one questioned. The religious creeds, while strict and barbarous, did not interfere with the personal conduct of any of the rulers. They were left free to act as they pleased, so long as they professed to believe in the prevailing faith.”

Introduction
An Enquiry into the Obligations of Christians (1792)
Context: In one period the grossest ignorance and barbarism prevailed in the world; and afterwards, in a more enlightened age, the most daring infidelity, and contempt of God; so that the world which was once over-run with ignorance, now by wisdom knew not God, but changed the glory of the incorruptible God as much as in the most barbarous ages, into an image made like to corruptible man, and to birds, and four-footed beasts, and creeping things. Nay, as they increased in science and politeness, they ran into more abundant and extravagant idolatries.

Some Mistakes of Moses (1879) http://www.gutenberg.org/files/38802/38802-h/38802-h.htm Preface
Context: Too great praise challenges attention, and often brings to light a thousand faults that otherwise the general eye would never see. Were we allowed to read the Bible as we do all other books, we would admire its beauties, treasure its worthy thoughts, and account for all its absurd, grotesque and cruel things, by saying that its authors lived in rude, barbaric times. But we are told that it was written by inspired men; that it contains the will of God; that it is perfect, pure, and true in all its parts; the source and standard of all moral and religious truth; that it is the star and anchor of all human hope; the only guide for man, the only torch in Nature's night. These claims are so at variance with every known recorded fact, so palpably absurd, that every free unbiased soul is forced to raise the standard of revolt.

On a children's hospital, Ch. III
Esther: A Novel (1884)

Why I Am An Agnostic (1929)

"Representación," San Carlos, 12 November 1800, Santa Bárbara Arch., 2:199-211.

Chrysippus, 3.
The Lives and Opinions of Eminent Philosophers (c. 200 A.D.), Book 7: The Stoics

Responding to audience questions during a speech in Detroit (1898); as recounted in Living My Life (1931), p. 207; quoted by Annie Laurie Gaylor in Women Without Superstition, p. 382
Context: Ladies and gentlemen, I came here to avoid as much as possible treading on your corns. I had intended to deal only with the basic issue of economics that dictates our lives from the cradle to the grave, regardless of our religion or moral beliefs. I see now that it was a mistake. If one enters a battle, he cannot be squeamish about a few corns. Here, then, are my answers: I do not believe in God, because I believe in man. Whatever his mistakes, man has for thousands of years past been working to undo the botched job your God has made.
As to killing rulers, it depends entirely on the position of the ruler. If it is the Russian Czar, I most certainly believe in dispatching him to where he belongs. If the ruler is as ineffectual as an American President, it is hardly worth the effort. There are, however, some potentates I would kill by any and all means at my disposal. They are Ignorance, Superstition, and Bigotry — the most sinister and tyrannical rulers on earth. As for the gentleman who asked if free love would not build more houses of prostitution, my answer is: They will all be empty if the men of the future look like him.

Heretics and Heresies (1874)

Source: The Winds of Limbo aka The Fireclown (1965), Chapter 4 (p. 151)