Dear Mr. Dawkins,
if I had ever doubted God’s existence, your book ‘The God Delusion’ would certainly have lead me to dispel my doubts. If you have no better arguments to offer than those which I found in your book, then the case for atheism must be really a weak one. From your own perspective, it might have been wiser not to write such a book: it simply exposes the untenability of your own worldview. Si tacuisses, philosophus mansisses.
I will not spend my time on giving you an exhaustive critique of your book here. I just want to point out to you what I view as your fundamental problem (apart from your personal anti-religious ressentiment, the roots of which must be hidden somewhere in your own biography): it is a thorough lack of philosophical education that prevents you from understanding the inherent limits of natural science and leads you to jump to conclusions that are not supported by any scientific findings. The non-existence of God is just such a conclusion.
Reading your book, one of your main targets seem to be ‘Creationists’, who believe that the universe has been created by God. You seem to affirm that this belief is disproved by what science has found out about evolution. But how do you disprove that evolution is a process that was triggered by a sovereign decision of God’s will?
You are worried about some Christian fundamentalists who believe in the literal truth of the account given in the Book of Genesis of the creation of the World during six days. In that regard, let me tell you that I personally (following the teaching of the Catholic Church, to which I adhere), have no problem at all with the Universe having been created some 13 billion, instead of 6000, years ago: bible fundamentalism is just not a part of the Catholic creed, and it never was. Instead, such fundamentalist tendencies are typical for American Protestants. It would have done good to your book to note and acknowledge such differences. But your real problem is: you are not even able to disprove the belief of these Creation-Within-6-Days-Fundamentalists. Your empiric science just does not suffice for disproving such beliefs: for if one believes in an almighty God, one can also believe in a God who 6000 years ago created a universe that was designed to look as if it were 13 billion years old. An ‘almighty’ God is certainly mighty enough to mislead the brightest scientific researchers. And how do you know that God has not done this?
What you need to rebuff the Creation-Within-6-Days-Theory is not only natural science, but also a philosophical/theological argument why God would not, on the one hand, endow man with reason, and on the other hand render his quest for truth futile: it would be self-contradictory for God to act in such a way. You find this reasoning in the famous Regensburg Lecture of Pope Benedict XIV., where he defended the principle that faith must be compatible with reason, and rejected the Islamic idea of a purely transcendent God. I recommend this text to your attention, for it will help you to understand the difference between reasonable and irrational belief.
Such an argument, however, is theological by nature; natural science serves neither to prove nor to disprove it. It is therefore Ratzinger’s argument that is needed to disprove Creation-Within-6-Days; a reasoning that remains within the remits of empiric science is not sufficient.
Let me therefore recommend you to follow a course in metaphysics before setting out to write books on subjects that are outside the field in which you may rightly claim to be an expert.