*Edit: Upon reflection, I find that "Christian Doctrine" is much too broad a brush to use in this context, as there are a great many Christians who believe a great many Doctrines. When I refer to it here, I simply mean the Christian Doctrine which I was taught and raised with- the Conservative Non-Denominational Christianity common to America*
Reasonable vs. True
Something being reasonable is not the same as that thing being true. For a position to be reasonable, all that is required is that it not be irrational for someone to hold such a position. For something to be true, it must actually conform to the nature and being of reality. Reasonability is therefore a much weaker standard than truth- many theories can be concurrently reasonable, but only one can be true. This leads directly to the notion that a theory can be reasonable but not true.
Notice that reasonable is a dynamic term- whether or not a belief is reasonable changes based on what data we currently have available. There was a time in which strict Newtonian physics was a reasonable theory. Newtonian physics, as it turns out, is a great approximation for physics operating at a scale within a few orders of magnitude of our own- anything from insects to a single planet. Before we had data that included observations about large bodies (planets) and small bodies (atoms), a person would be rationally justified believing the Newtonian model was correct (insofar as we believe any theory about the physical world to be correct). It was, of course, eventually superseded by Quantum Mechanics and Relativity, which better explain such phenomena. Newtonian physics was rational, but ultimately not true. (Not true on the grander scale, that is. Newtonian physics is still an applicable theory, but in a much more limited scope than it once was)
It is also, curiously, possible for something to be true but not reasonable. The Platypus is perhaps my favorite example. Even its discoverers had trouble accepting that an egg-laying, venomous, duck-billed, beaver-tailed, otter-footed mammal existed, because it flew in the face of so many evolutionary norms. To presuppose such an animal without evidence would not be rational, and so a belief in a Platypus-like creature would have been an unreasonable belief before the discovery of the animal itself, much like a modern day belief in the Chupacabra, the Yeti, the Unicorn or Bigfoot. These are unreasonable beliefs to hold, but that does not make any of them patently untrue.
Message vs. Doctrine
I would also like to differentiate the Christian Message from Christian Doctrine. The Christian Message is what Lewis argues for in "Mere Christianity"- that there is an objective moral standard, that there is a God, that humans are broken, that we need reconciliation with that God, and that Jesus was the vehicle of that reconciliation. The Christian Message is short, pure, and it seems to resonate very strongly with people (myself included)
The Christian Doctrine is another beast altogether. It contains a great many claims (A 10,000 year old earth, a non-evolutionary creation cycle, a global flood, the inerrancy of Biblical text, and a great many old testament laws that make the true believer blush) that are either unsubstantiated or flat out in contradiction with modern scientific understanding.
Is it possible to reconcile these claims against the world we observe? Maybe. Most Christians do it by denying the facts (evolution, the fossil record, cosmology, etc.) and explaining moral inconsistencies as cultural norms. As I said in my accepted axioms, I believe that if science contradicts faith, we ought take the side of science. Is it possible to discount Genesis (or indeed, much of the old testament), as exactly what it is- an oral history of the nation of Israel- rather than as the unaltered spoken word of God? Maybe. I think it depends on how Jesus treats this part of the scripture. If he claims it is inerrant and from the mouth of God, then either Jesus was wrong or every scientific observation we've made for the last 100 years was put there by God himself to test us - or rather to intentionally confuse us! If Biblical inerrancy is a claim made by others, a claim made by the modern church even, then perhaps there is a non-literal interpretation of old testament scriptures that can coexist with modern scientific knowledge? But I digress- I will examine what I believe to be the scientific conflicts of the Christian Doctrine in a later post
In regards to the Christian Message, I find it to be reasonable. It is not scientific, nor does it claim to be, but I can conceive of a framework of existence in which Christianity is in fact true. It is not therefore inherently irrational to accept the Christian Message. If it is in fact true, however, we would expect to see some observable consequences. We would expect that, upon accepting Christ, we would feel the active and real self-authenticating presence of the Holy Spirit in our lives. This is the evidence I lacked the last time around, and the reason I walked away. But again, I digress.
In regards to the Christian Doctrine, I find it to be unreasonable. To accept as true unsubstantiated scientific claims at the expense of substantiated ones is the sign of a dogmatic faith, a blind faith. The Christian will claim that their faith is not blind, but justified by experiential evidence- and rightly so, for experiential evidence is what Christian theologians, the Bible, and Christ himself claims to offer. However, Christians who make this claim must recognize that they are accepting the entirety of the Christian Doctrine because specific parts of it (forgiveness of sin, salvation by grace, freedom in Christ, etc.) ring true to them. Christians, however, have no more experiential evidence for the beginning of the universe than Atheists do. Moreover, where atheists have a plethora of scientific evidence, Christians have essentially none whatsoever supporting their claims about creation. Belief in such things is therefore an appeal to Authority, not an appeal to reason. Rather, it is an appeal to Authority in direct contradiction to evidence.
It should be noted that I have had several conversations with Christians who assure me that no, the evidence really does support the Biblical view. However, in the research I've done so far, the Atheist offers much more compelling arguments, much stronger evidence, and a much more comprehensive view of the facts in regard to the early history of the earth (to say nothing about the historicity of the flood). It seems to be the case that almost no serious scientists without a significant bias (and let us be honest here and admit that the Christian Doctrine is a steep bias) doubt the common descent model of Evolution. Third digression is the charm. My problems with the Christian Doctrine will receive several posts later on.
The Christian Doctrine was, historically, reasonable. For a long time, there was no reason to doubt the age of the universe was a few thousand years old, no reason to suspect that all life shows signs of common descent. But new data, particularly data gathered in the last 150 years, has changed our understanding of the world. If the Christian Doctrine cannot coexist with this new data, then it is not the data we ought reject.