Photo: ©  2010 AAP/DEAN LEWINS

Sydney's Anglican Archbishop Peter Jensen used his address at St Andrew's Cathedral to slam atheism as "a form of idolatry in which we worship ourselves" and an "assault on God".

"As we can see by the sheer passion and virulence of the atheist - they seem to hate the Christian God - we are not dealing here with cool philosophy [but are] up against faith without a brain."

The Catholic Bishop of Parramatta, Anthony Fisher, went even further, blaming disbelievers for fascism.

"[It's] the illusion that we can build a better life without God," he told worshippers.

"Last century, we tried godlessness on a grand scale and the effects were devastating: Nazism, Stalinism, Pol Pot-ery, mass murder, abortion and broken relationships - all promoted by state-imposed atheism."

The attacks come on the back of Richard Dawkins' Rise of Atheism conference in Melbourne last month, which was attended by 2,500 people.