Guardian Angel - no intelligent atheist denies the *possibility* of the existence of God, any more than he denies the possibility of Little Green Men existing. All he denies is that this belief is remotely probable, given the current evidence available.
We therefore must examine what underpins the rationality of beliefs.
The atheist claims that rational human beings judge the truth or falsity of a belief by assessing i) the amount of credible evidence in favour of it ii) the absence of alternative explanations for the belief, which are more consistent with our current understanding of the universe. This is the basis of Hume's argument for assessing the likely truth or falsity of "miraculous"/outlandish claims about reality (of which religion is only one - the same test would be applied to Columbus' first discovery of America, or a claim to have seen the Yeti, or to have turned $1000 into $10 million in 18 months by daytrading)
If, after assessing the credibility of the evidence in favour, versus the credibility of alternative explanations, he thinks that the latter are overwhelmingly more credible and probable than the former, (given our understanding of the way the world works) then he rejects the belief. I don't see how there is anything irrational about rejecting a belief with a very low probability. One must always keep an open mind to the *possibility* that the belief is in fact true against the apparent odds, but it is quite reasonable to go around living on the basis that, whilst possible, it is nontheless extremely unlikely to be true.
Now, you and others have argued that this is irrational and unjustifiable, and in response I have asked on what grounds, then, do you refuse to believe in Little Green Men, or (for example) miraculously profitable trading systems?
Presumably you reject those beliefs not because you think that that Hume's test of outlandish & miraculous claims is irrational, but because you believe the evidence in favour of their existence is of far lower credibility than alternative explanations which fit far better with our understanding of how the world works - for example, given our knowledge of human greed and the difficulty of trading, it is far more likely that an outlandish trading claim is intended to sell worthless trading systems, newsletters etc, then it is to be true. Therefore we *rationally* reject the belief, despite being completely unable to *prove* that it is untrue. We use probability and credibility, NOT 100% proof, to make a rational decision under conditions of uncertain knowledge.
So, given that you presumably use exactly the same methodology to judge outlandish claims unsupported by credible evidence, and presumably do not consider yourself irrational, how can you consistently claim that to use exactly the same approach to judge the existence of religion is irrational, just because it cannot be *proven* that religion is untrue?
You have basically set up a straw man, using incorrect assumptions about how atheists use reasoning, and then judged their set of beliefs under one set of standards, while judging your own beliefs under a far more lax set of standards. This is logically inconsistent - starting from a point of scepticism, clearly a rational person must apply the *same* standards to his assessment of all beliefs.
So - do you accept that it is rational to assign a low probability to a belief, IF one judges the evidence for it to be far outweighed by the evidence against it? If so, then you accept that "atheism" (or "hard agnosticism" - whatever you want to label it) can be rational for a person who judges the evidence for religion to be tenuous.
Now, if you accept that assumption (and if not, you must provide evidence *why* you do not), then we can move on to a discussion of the evidence available, and try to make a rational assessment of its credibility, applying the same standards we would to an assessment of any other type of evidence for any other type of belief.
I have provided some examples of evidence against, you have provided some for. But let us now make posts clearly listing *only* our evidence for and against - then let everyone judge the arguments in favour and against the credibility of that evidence.
