One quick thought to add: I've often seen it stated by theists over the years that atheism is the positive claim that gods do not or cannot exist. William Lane Craig famously begins many of his debates by asking, "What is the evidence for atheism?", conflating atheism with some sort of philosophy. When atheists 'admit' they cannot prove there are no gods, he says they are merely 'agnostics'. QualiaSoup has another great video on this topic – the Lack of Belief in Gods.
Theists like WLC are overlooking the fact that agnosticism and atheism answer different questions – "gnosis" meaning knowledge, and atheism dealing with belief. We can say:
- There is no evidence that gods exist, therefor I remain agnostic until evidence is presented
- Because there is no evidence, I do not hold a positive belief that gods exist, thus I am an atheist
There is, however, one positive claim entailed by atheism that I think does need to be defended: that our beliefs ought to be derived solely from empirical evidence – and that things like faith and revelation are not a valid basis for forming beliefs. I made just such a defense recently in my post The Importance of Evidence.