To one who knows God faith is entirely logical. What rules do you use to claim that those who know God in their hearts do not know God? How do you claim to know that they do not Know?
Because plenty of people of plenty of different, mutually exclusive, religions make such claims and they can't all be right. But they can all be wrong.
Coupling that with everything we know about psychology and psychiatry - from full blown hallucinations to the common and less impactfull "imaginary friends" - and the knowledge of how people are easily fooled, easily make mistakes, easily misinterpret things that happened to them, how easily humans see patterns where there are none, how narcistic they are, etc.....
It becomes almost impossible to take people's word for it when they make such claims.
When we have such a myriad of not only possible, but
plausible, explanations about their "experiences" and "beliefs" that they can't demonstrate in any possible way.....
It's a LOT more rational to assume they are delusional / mistaken then to assume that the most implausible, most illogical and most unsupportable option of "god" is actually correct.
And even IF we would assume that it the god bit is indeed correct, we are still left wondering "which god?". Because as I've said, they can't ALL be right (but they CAN all be wrong).
How can we go about deciding if the claim of the muslim is correct as opposed to the claim of the christian, the jew, the hindu,...?
We can't. So even IF we would go with the
least likely and the most implausible, we still have no way of differentiating between all those thousands of different claims. And we will be left with having to arbitrarily choose one of them.
None of that makes sense. None of that is rational.
Going with the most plausible explanation is what is rational.
And that explanation is that all those theistic claims are mistaken.