Bertrand Russell -- philosopher, logician, mathematician, historian, and social critic -- was one of the greatest thinkers of the 20th century.
For most of his adult life, Russell maintained that religion is little more than superstition and, despite any positive effects that religion might have, it is largely harmful to people. He believed religion and the religious outlook (he considered communism and other systematic ideologies to be forms of religion) serve to impede knowledge, foster fear and dependency, and are responsible for much of the war, oppression, and misery that have beset the world.
Russell's Why I am Not a Christian was a strong factor in the loss of my faith in Christianity.
Some of my favorite observations by Russell include:
"So far as I can remember, there is not one word in the Gospels in praise of intelligence."
"A hallucination is a fact, not an error; what is erroneous is a judgment based upon it."
"Fear is the main source of superstition, and one of the main sources of cruelty. To conquer fear is the beginning of wisdom."
"The objections to religion are of two sorts - intellectual and moral. The intellectual objection is that there is no reason to suppose any religion true; the moral objection is that religious precepts date from a time when men were more cruel than they are and therefore tend to perpetuate inhumanities which the moral conscience of the age would otherwise outgrow."
"Wherever there is power, there is a temptation to encourage credulity in those who are subject to the power in question."
"I say quite deliberately that the Christian religion, as organized in its Churches, has been and still is the principal enemy of moral progress in the world."
"I would never die for my beliefs because I might be wrong."
"I think we ought always to entertain our opinions with some measure of doubt. I shouldn't wish people dogmatically to believe any philosophy, not even mine."
"Man is a credulous animal, and must believe something; in the absence of good grounds for belief, he will be satisfied with bad ones."
"Many people would sooner die than think; in fact, they do so."
"Religions, which condemn the pleasures of sense, drive men to seek the pleasures of power. Throughout history power has been the vice of the ascetic."
"The infliction of cruelty with a good conscience is a delight to moralists. That is why they invented Hell."
"The world is full of magical things patiently waiting for our wits to grow sharper."