So, if his thinking were really that 'critical', he should be able to recognize that he has nothing to debate with. That, in fact, there is nothing to debate.
But any belief or opinion a person makes in a public forum can be assessed and commented on. Whether it is total faith-based nonsense or a claim that has facts and a coherent argument a critical thinker can offer a reasoned comment. That's what many of us do. Theists in debate tend to think their beliefs are to be accepted at face value, as they have adopted these ideas as true without facts or a reasoned conclusion. Their beliefs are just the TRUTH. Not to be questioned. But we do.
Faith is a personal, subjective choice based on the personal subjective results that one derives from having made that choice and lived with it a while. What is there to debate? What is there to rebut? Especially when the 'critic' has no similar experience of his own from which to enter what is an essentially subjective dialogue?
We ask questions all the time that aim to dig deeper than this superficial choice you present. Why do theists think they make these choices to believe a specific version of god exists? Why that version and not some other version? Science explains how religious thinking and rituals makes the reward center of the brain light up, so this explains why ritual can become a habit, and the euphoria of hormones in the blood feels good. I'm curious how believers feel about that, being caught in a cycle of think-reward. Do you as a theist have any interest in this physical phenomenon, and how it might explain why you have religious experiences that are likely just hormones?
And the amazing thing, to me, is that these "critical thinkers" never see this most obvious fault. And instead, they just bulldoze onward, insisting on evidence and facts and objective reasons and so on. Oblivious that they are not even within the realm of subject that they think they are rebutting.
It's that theists are shown the inner workings of how they think, but ignore the truth of it because the belief and the resulting condition feels good. I'm curious if a theist will ever stop and actually choose to examine why they believe at all instead of being content with the illusion they maintain, as "a personal, subjective choice".