As to the question:
'Is Atheism based on Logic or Faith?'
It seems to be based on neither logic or faith but on ignorance, especially if one believes that it is the 'default setting' of a human individual.
Some might agree with you. Consider the following definitions.
gnostic: one with knowledge of a deity
agnostic: one without knowledge of a deity
theist: one with belief in a deity
atheist: one without belief in a deity
If one were to say that he was without knowledge of a deity, then he could be considered to be ignorant. He would also be agnostic as defined above.
If he went on to say that, because he has no knowledge of a deity he cannot say that a deity exists, and that therefore he is without belief in a deity, then he would be an atheist.
In a simplified case such as this, one could say that atheism is based in ignorance. Of course, not everyone will agree with the definitions above, and not all paths to atheism follow the same lines of thought.
For instance, others might argue that they are extremely well-read as far as literature regarding deities is concerned. They might dismiss the notion that deities exist based on the fact that there is overwhelming evidence in support of the notion that deities are fictitious entities, coupled with the fact that there is
no compelling evidence that they exist. These folks might not agree that atheism is based in ignorance. So it may not be as simple as outlined above.
BTW: Ignorance is not a bad thing, unless you're pretending to have knowledge that you don't actually have. IMO, of course--