Let's use this functional definition of deity or "god":
A sacred reality which is a reality that is fundamentally and substantively other than that which is constrained by the set of all cause and effect, yet actively engages in the set of all cause and effect in relationship to it.
In scientific terms, any object that is outside of the set of all cause and effect simply cannot exist. To posit such an object is for all intents and purposes absurd. Kant made this observation regarding how the human mind works, how reason functions, and the nature of God as that which cannot be known in terms of cause and effect relationships. God's existence is outside of space and time and anything outside of space and time is beyond the limits of reason.
This Kantian understanding of God is largely where the neo-atheists of today start off with their arguments contra the existence of God. Framed this way with these foundational criteria, there is no where for a believer in God to go. Any belief in God will never meet the criteria for rationality required here.
Of course, Kierkegaard went in a radically different direction. While after Kant, Hegel would posit the idealism of the unfolding of "spirit" through the necessity of history, Kierkegaard ran past Hegel's necessity to focus on choice. In this sense Kierkegaard re-grounds belief in God in the behavior of choice, but not by choosing what is most rational. Rather it is choosing what appears to be absurd only to find on the other side of the choce that it is the only rational outcome one could have made in the first place. Choosing God appears to be something very absurd, but it is in the end quite rational. The point is that one has to make the choice.
For Dawkins and others choosing God is absurd. It is also at the heart of what it means to be irrational and so, one ought not choose it. To that Kierkegaard would agree. However, not to choose the absurd in this case is not rational. This cannot be made through a rational argument, but ony through a leap of faith. It is only on the other side of that choice that we understand we have made a rational decision. Dawkins would consider this foolish to be sure. He is right from his point of view. But what seems to us to be foolish on his criteria of rationality may in fact be the best choice possible.
While many atheists will use the bible to say that God is evil, it is full of absurd tales of magic, rape, etc. The one bit that perhaps they cannot accept is that for most believers in God or in some sort of deity, that belief is ultimately rooted in the experience one has with that deity, or with that sacred reality – not on the sole basis of a text. Evidence shows that even among fundamentalists who appear to rely only on the bible for their faith (or a kind of interpretation of the bible) experience is what actually mediates that understanding of the bible. One side will determine this experience to be delusional and no amount of evidence can be convincing. It is the choice in the face of the absurd to believe in God that mediates the kind of belief one has. Many continue to make that choice on a regular basis. To them not making that choice is, ironically, something that would be evidence of irrational and irresponsible behavior.
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