Folks, I’d like to place here what I believe is the strongest argument for atheism, and I invite you to attack it or suggest improvements.
For the purpose of the thread, feel free to take positions contrary to your personal beliefs for the purpose of honing your skills and improving the argument.
The main argument goes like this:
Let’s define “faith” as a way of learning about things through personal revelation. I place no judgement as to whether this is insight generated by the individual, or received from a divine or supernatural source.
Faith can be contrasted with the scientific method, which is a process of using empirical observation to learn about things.
All religions which make claims about the state of the world (in particular the existence of a god, and participation of the god in the world in some way) base these claims on faith. This true in general, but it is also true in the case of religions which include a written text as a record of beliefs. Most of the knowledge in these texts is, even if accepted at face value, based on personal faith of the authors.
Personal revelation is also required to interpret the texts and to select which portions are allegorical, which portions are claims of fact, and which portions are known to the authors by faith. This is necessary because at face value the texts contain self contradictions and contradictions with known historical and empirically confirmed facts.
Faith also receives attention as a virtue in many but not all religions. (I believe in all monotheistic or quasi-monotheistic religions faith is a virtue).
The scientific method as a way of knowing about things has itself been empirically confirmed as effective. Unless a complete position of solipsism is adopted, this is not circular. Since in a state of complete solipsism there is no way of knowing about anything, faith is also excluded, and so solipsism is not a relevant consideration in the theist/atheist argument. We know that the scientific method is reliable because the knowledge we obtain from it allows confident prediction of the behaviour of the physical world.
Faith has been established as an unreliable method of knowing. All religious beliefs which are consistent with the current known state of the physical world are inconsistent with historical religious beliefs - ie, almost the entire portion of revealed knowledge which has been subject to observation and measurement has been shown to be incorrect.
Faith, when applied to the same empirical knowledge (including knowledge of the existence and content of religious texts) is not repeatable - different people come to very different conclusions, which can be shown to correlate with the dominant religious beliefs they are exposed to.
The conclusion is that all belief in a god is gained from a method of knowing which has been proven to be unreliable. No alternate methods of knowing have been able to confirm beliefs in a god, despite the fact that most beliefs about god are capable of generating testable hypotheses about the effects of the existence of god on the state of the world.
Following from this, it is more reasonable to believe that there is probably no god than to believe that there is probably a god.
Further, there is no reliable way to gain knowledge about a god, even should one exist. Hence, belief in any specific attributes, behaviour or intent of a god is highly irrational.
Interestingly, if one already has a belief in a god, it is not necessarily irrational to maintain that belief, if one also believes that the cost of seeking information or reasoning exceeds the benefit of more reliable knowledge.
However, making considerable effort to maintain a belief in a god is irrational (since it involves cost with no improvement in knowledge).
(As an aside to this argument, it is this last point that leads me to lose respect for Christian apologetics. I have no problem with people of faith who are quite happy believing and see no need to question their beliefs).