Since I’m often asked this question, I thought it might be wise to make an answer available for everyone to reference. As in a previous post, this will not be an in depth debunking of every religion, but a summarized if brief, overview of my position.
The Atheist Position
No sufficient evidence has ever been adduced to suggest that any deity is real. From the Greek Gods to Christianity and Islam, no evidence has ever been produced by the proponents of these religions to think that they are any more likely than any other mythology.
What evidence we do have, in fact, goes the other way. From the early books of the Christian Old Testament, the evidence immediately starts to diverge from the accounts posited by Christianity. From the science of biology which shows that the species we see today, were not created in their current form but the result of a extremely long and complex process of trial and error, extinctions and explosions of life. From recorded history, archeology and other disciplines, the evidence clearly shows that most of the events of the Christian religion, simply did not occur and show signs that parts were probably borrowed and assimilated from older civilizations and religions.
There are moral difficulties with religion and the deities they describe as well. The salient fact of the matter is, that even if the bible and koran were true, it would make no difference to myself and many other atheists. We would acknowledge that Yahweh does exist, but we would still not worship him. The god Yahweh, as described by the Christians, is an immoral character of horror and indiscriminate cruelty. The Muslim version of this character is just as bad off.
This is not to say that, no god can exist. I and many other atheists will tell you that, we can not say that a god, somewhere, doesn’t exist. It’s an unfalsifiable claim and there is no way to disprove that premise. But I have no problem saying that the Jewish deity, along with it’s Christian and Islamic instantiations, do not exist.