Suppose I am a theistic scientist, and I come up with a simple and elegant theory that fits the data. You ask me:
- But what reason do you have to believe that the theory is true?
- There is a good God who created a world exemplifying genuine values like simplicity and beauty.
- If (2) is true, its truth significantly raises the probability that a simple and elegant theory that fits the data is true.
If this is right, then you will have cases where a theist and atheist scientist agree on the scientific evidence, but the theist weakly assents to the theory but the atheist is more skeptical of the scientific theory.
In general, assuming rationality on both sides, we would expect atheists to be significantly more sceptical of scientific claims than theists who, in turn, should be bolder theorizers. But I think we do not observe this. Hence, on one or both sides, there is some irrationality—or else I am wrong about (3).