I recently came across this fantastic open source document on Anarchism called The Anarchist FAQ. It has been in development online since 1996, and is constantly being updated. Anarchism (which almost by pure semantic default) has rationalism, liberty and atheism as core values has been, like atheism, the subject of slander, distortion, and misrepresentation - from both left and right wing groups - since its beginnings:

"[Anarchists are] the radical of the radical -- the black cats, the terrors of many, of all the bigots, exploiters, charlatans, fakers and oppressors. Consequently we are also the more slandered, misrepresented, misunderstood and persecuted of all." [Nicola Sacco and Bartolomeo Vanzetti, The Letters of Sacco and Vanzetti, p. 274]

Since many western democracies are in the grip of irrational religion(s), irrational consumerism (a possibly more fatal condition when combined with faith) ands high levels of concentrated unaccountable private power, the anarchist society may well remain a utopian dream. However the level of thought and consistency within anarchism is worth paying attention to as we battle the forces of dogmatic absurdity in this world.

In light of this I have posted a very relevant section from this document. Enjoy.

The source is available here, and a Wiki article on this essay is here.

Tim. 

A.2.20 Why are most anarchists atheists?

It is a fact that most anarchists are atheists. They reject the idea of god and oppose all forms of religion, particularly organised religion. Today, in secularised western European countries, religion has lost its once dominant place in society. This often makes the militant atheism of anarchism seem strange. However, once the negative role of religion is understood the importance of libertarian atheism becomes obvious. It is because of the role of religion and its institutions that anarchists have spent some time refuting the idea of religion as well as propagandising against it.

So why do so many anarchists embrace atheism? The simplest answer is that most anarchists are atheists because it is a logical extension of anarchist ideas. If anarchism is the rejection of illegitimate authorities, then it follows that it is the rejection of the so-called Ultimate Authority, God. Anarchism is grounded in reason, logic, and scientific thinking, not religious thinking. Anarchists tend to be sceptics, and not believers. Most anarchists consider the Church to be steeped in hypocrisy and the Bible a work of fiction, riddled with contradictions, absurdities and horrors. It is notorious in its debasement of women and its sexism is infamous. Yet men are treated little better. Nowhere in the bible is there an acknowledgement that human beings have inherent rights to life, liberty, happiness, dignity, fairness, or self-government. In the bible, humans are sinners, worms, and slaves (figuratively and literally, as it condones slavery). God has all the rights, humanity is nothing.

This is unsurprisingly, given the nature of religion. Bakunin put it best:

"The idea of God implies the abdication of human reason and justice; it is the most decisive negation of human liberty, and necessarily ends in the enslavement of mankind, both in theory and in practice.

"Unless, then, we desire the enslavement and degradation of mankind . . . we may not, must not make the slightest concession either to the God of theology or to the God of metaphysics. He who, in this mystical alphabet, begins with A will inevitably end with Z; he who desires to worship God must harbour no childish illusions about the matter, but bravely renounce his liberty and humanity.

"If God is, man is a slave; now, man can and must be free; then, God does not exist." [God and the State, p. 25]

For most anarchists, then, atheism is required due to the nature of religion. "To proclaim as divine all that is grand, just, noble, and beautiful in humanity," Bakunin argued, "is to tacitly admit that humanity of itself would have been unable to produce it -- that is, that, abandoned to itself, its own nature is miserable, iniquitous, base, and ugly. Thus we come back to the essence of all religion -- in other words, to the disparagement of humanity for the greater glory of divinity." As such, to do justice to our humanity and the potential it has, anarchists argue that we must do without the harmful myth of god and all it entails and so on behalf of "human liberty, dignity, and prosperity, we believe it our duty to recover from heaven the goods which it has stolen and return them to earth." [Op. Cit., p. 37 and p. 36]

As well as the theoretical degrading of humanity and its liberty, religion has other, more practical, problems with it from an anarchist point of view. Firstly, religions have been a source of inequality and oppression. Christianity (like Islam), for example, has always been a force for repression whenever it holds any political or social sway (believing you have a direct line to god is a sure way of creating an authoritarian society). The Church has been a force of social repression, genocide, and the justification for every tyrant for nearly two millennia. When given the chance it has ruled as cruelly as any monarch or dictator. This is unsurprising:

"God being everything, the real world and man are nothing. God being truth, justice, goodness, beauty, power and life, man is falsehood, iniquity, evil, ugliness, impotence, and death. God being master, man is the slave. Incapable of finding justice, truth, and eternal life by his own effort, he can attain them only through a divine revelation. But whoever says revelation, says revealers, messiahs, prophets, priests, and legislators inspired by God himself; and these, as the holy instructors of humanity, chosen by God himself to direct it in the path of salvation, necessarily exercise absolute power. All men owe them passive and unlimited obedience; for against the divine reason there is no human reason, and against the justice of God no terrestrial justice holds." [Bakunin, Op. Cit., p. 24]

Christianity has only turned tolerant and peace-loving when it is powerless and even then it has continued its role as apologist for the powerful. This is the second reason why anarchists oppose the church for when not being the source of oppression, the church has justified it and ensured its continuation. It has kept the working class in bondage for generations by sanctioning the rule of earthly authorities and teaching working people that it is wrong to fight against those same authorities. Earthly rulers received their legitimisation from the heavenly lord, whether political (claiming that rulers are in power due to god's will) or economic (the rich having been rewarded by god). The bible praises obedience, raising it to a great virtue. More recent innovations like the Protestant work ethic also contribute to the subjugation of working people.

That religion is used to further the interests of the powerful can quickly be seen from most of history. It conditions the oppressed to humbly accept their place in life by urging the oppressed to be meek and await their reward in heaven. As Emma Goldman argued, Christianity (like religion in general) "contains nothing dangerous to the regime of authority and wealth; it stands for self-denial and self-abnegation, for penance and regret, and is absolutely inert in the face of every [in]dignity, every outrage imposed upon mankind." [Red Emma Speaks, p. 234]

Thirdly, religion has always been a conservative force in society. This is unsurprising, as it bases itself not on investigation and analysis of the real world but rather in repeating the truths handed down from above and contained in a few holy books. Theism is then "the theory of speculation" while atheism is "the science of demonstration." The "one hangs in the metaphysical clouds of the Beyond, while the other has its roots firmly in the soil. It is the earth, not heaven, which man must rescue if he is truly to be saved." Atheism, then, "expresses the expansion and growth of the human mind" while theism "is static and fixed." It is "the absolutism of theism, its pernicious influence upon humanity, its paralysing effect upon thought and action, which Atheism is fighting with all its power." [Emma Goldman, Op. Cit., p. 243, p. 245 and pp. 246-7]

As the Bible says, "By their fruits shall ye know them." We anarchists agree but unlike the church we apply this truth to religion as well. That is why we are, in the main, atheists. We recognise the destructive role played by the Church, and the harmful effects of organised monotheism, particularly Christianity, on people. As Goldman summaries, religion "is the conspiracy of ignorance against reason, of darkness against light, of submission and slavery against independence and freedom; of the denial of strength and beauty, against the affirmation of the joy and glory of life." [Op. Cit., p. 240]

So, given the fruits of the Church, anarchists argue that it is time to uproot it and plant new trees, the trees of reason and liberty.

That said, anarchists do not deny that religions contain important ethical ideas or truths. Moreover, religions can be the base for strong and loving communities and groups. They can offer a sanctuary from the alienation and oppression of everyday life and offer a guide to action in a world where everything is for sale. Many aspects of, say, Jesus' or Buddha's life and teachings are inspiring and worth following. If this were not the case, if religions were simply a tool of the powerful, they would have long ago been rejected. Rather, they have a dual-nature in that contain both ideas necessary to live a good life as well as apologetics for power. If they did not, the oppressed would not believe and the powerful would suppress them as dangerous heresies.

And, indeed, repression has been the fate of any group that has preached a radical message. In the middle ages numerous revolutionary Christian movements and sects were crushed by the earthly powers that be with the firm support of the mainstream church. During the Spanish Civil War the Catholic church supported Franco's fascists, denouncing the killing of pro-Franco priests by supporters of the republic while remaining silent about Franco's murder of Basque priests who had supported the democratically elected government (Pope John Paul II is seeking to turn the dead pro-Franco priests into saints while the pro-Republican priests remain unmentioned). The Archbishop of El Salvador, Oscar Arnulfo Romero, started out as a conservative but after seeing the way in which the political and economic powers were exploiting the people became their outspoken champion. He was assassinated by right-wing paramilitaries in 1980 because of this, a fate which has befallen many other supporters of liberation theology, a radical interpretation of the Gospels which tries to reconcile socialist ideas and Christian social thinking.

Nor does the anarchist case against religion imply that religious people do not take part in social struggles to improve society. Far from it. Religious people, including members of the church hierarchy, played a key role in the US civil rights movement of the 1960s. The religious belief within Zapata's army of peasants during the Mexican revolution did not stop anarchists taking part in it (indeed, it had already been heavily influenced by the ideas of anarchist militant Ricardo Flores Magon). It is the dual-nature of religion which explains why many popular movements and revolts (particularly by peasants) have used the rhetoric of religion, seeking to keep the good aspects of their faith will fighting the earthly injustice its official representatives sanctify. For anarchists, it is the willingness to fight against injustice which counts, not whether someone believes in god or not. We just think that the social role of religion is to dampen down revolt, not encourage it. The tiny number of radical priests compared to those in the mainstream or on the right suggests the validity of our analysis.

It should be stressed that anarchists, while overwhelmingly hostile to the idea of the Church and an established religion, do not object to people practising religious belief on their own or in groups, so long as that practice doesn't impinge on the liberties of others. For example, a cult that required human sacrifice or slavery would be antithetical to anarchist ideas, and would be opposed. But peaceful systems of belief could exist in harmony within in anarchist society. The anarchist view is that religion is a personal matter, above all else -- if people want to believe in something, that's their business, and nobody else's as long as they do not impose those ideas on others. All we can do is discuss their ideas and try and convince them of their errors.

To end, it should noted that we are not suggesting that atheism is somehow mandatory for an anarchist. Far from it. As we discuss in section A.3.7, there are anarchists who do believe in god or some form of religion. For example, Tolstoy combined libertarian ideas with a devote Christian belief. His ideas, along with Proudhon's, influences the Catholic Worker organisation, founded by anarchists Dorothy Day and Peter Maurin in 1933 and still active today. The anarchist activist Starhawk, active in the current anti-globalisation movement, has no problems also being a leading Pagan. However, for most anarchists, their ideas lead them logically to atheism for, as Emma Goldman put it, "in its negation of gods is at the same time the strongest affirmation of man, and through man, the eternal yea to life, purpose, and beauty." [Red Emma Speaks, p. 248]