Following on from my previous blog, I think the crutial point is faith.
I think Stephen is right in that any point of view can be a faith (http://stephenlaw.blogspot.com/ - Faith topic), and that's certainly the case for most, if not all, religions. And I personally know at least one person for whom atheism is a faith. She has no interest in any arguments one way or the other, and certainly has no interest in science, but believes herself to be endowed with ultra reliable common sense, to the extent that she believes the whole God business is nonsense. It's as if this faith of hers has grown out of some dissatisfaction with religion and all its trappings, a discomfort in the presence of religious people and proceedings. And I detect a similar discomfort in the absence of religion, or in the company of atheists, in some religious people. The opposing point of view is dismissed out of hand, with little discussion. Whichever way you lean this is a pretty insecure faith.
The faith expressed by professional theologians and serious theists appears to be much stronger, both in intensity and in the degree of thought put into it. I think that this is the type of religious faith with which atheism is competing; but which atheism? Not the atheism promoted by the feeble faith atheists - the faith atheism that theists attack, but scientific atheism. And this scientific atheism isn't a faith, though it is a belief system.
With the strong theological faith, when all the trappings are stripped away, when all the arguments of reason against it have been put forward and dismissed, what is left is pure and absolute faith. An explanation is not required. That's it. No argument.
Science based atheism isn't that. And in not being that, it isn't a faith, or not a strong faith. Science based atheism relies entirely on empiricism at its base. And in that it is, and will always be, open to doubt and question. I don't mean the personal doubt that one might have in any belief system, but an underlying inherent doubt in the system itself. Every currently understood 'fact' upon which all science is based is ultimately in doubt. The limitations of its tools of deduction and induction are often pointed out by the faith followers, and rightly. Most arguments are circular and nothing is conclusive. There is no absolute - though for practical reasons it may often be convenient to act is if there is.
But not only all that; there's another element of the science that is at the heart of science based atheism: the requirement for Popper's falsificationism. Science, and scientific based atheism requires this. Not just now, to ensure that for some current theory to be valuable it must be falsifiable, but in perpetuity. No matter how far into the future we look, no matter to what extent we evolve, whatever answers we find, there will always be something we don't know, or cannot know at that time.
To put it simply, I have no absolute faith in my current belief in science based atheism, but I do believe it, because all the current evidence I have tells me it's the best choice for a belief system.
So, does God exist? Theist faith tells me he does, but gives me no reason to believe it, so why should I. Science merely tells me he probably doesn't, but gives me very good reason for believing he doesn't.
Neither point of view has any baring on the existence of God. He exists or he doesn't, irrespective of which belief system one follows.
And, his existence or not has little consequence for the two belief systems. If God doesn't exist then it won't matter to the religious. They can go on believing and they'll never know. As each draws his terminal breath that'll be the end of him. And for the scientific atheists there's not even the satisfaction that we haven't yet been proved wrong, because our position will remain the same - he still might exist. An if he does exist, there's no change for the faithful - they knew it all along. If they find he exists I hope there won't be too much gloating, as that would imply they weren't as sure as they've been saying they were before his existence became evident. And for the scientific? Maybe no longer strictly atheists, since being true to our principles we should be happy to accept the new evidence - just not absolutely.