First things first, in a reasoned discussion theists never stick to reason, ever
That's a generalization. If you were talking about theists who adamantly believe that the earth was created in 7 days a few thousand years ago in the face of all scientific evidence that points to the contrary, then yes, these theists cannot stick to reason.
Theistic evolutionists. These are theists that accept evolution as a scientific fact but also believe in intelligent design. I would personally place myself in that category.
We are faced with an overwhelming amount of scientific evidence that ultimately do contain divine implications which I have posted many times before on this forum.( The cosmological theory, the fine-tuning theory). Also, and perhaps even more importantly, there are philosophical questions that point to the divine.
Why is there something rather than nothing? Can non-life give birth to life given an infinite amount of time? If I built a wooden chair, can it turn into an animal a few hundred million years from now .Are physical laws man-made(constructivism) or are they part of nature? If they are an innate part of nature, who or what set up these laws?
There a countless number of questions one can ask about the nature of life that would really point to God, and would get an atheist thinking, It did so to the most prominent and influential atheistic figure in the past century, Antony Flew.
It's very unintelligible to label theistic arguments irrational or unreasonable. I would agree with Martin here that much of the scripture is filled with contradictions, at least this is what it seems. But this is not what I am personally interested in, I am more inclined to exploring the possibility/plausibility of God's existence.