I think capsium makes a good point here. To be truly a critical thinker means that you allow the possibility that your views will be changed by what another person says -- and that is never a comfortable process. It is very hard to admit that your own cherished views might be wrong, and that you might have to change them. It is very hard, too, to see cognitive dissonance as positive, because it isn't comfortable. But the ability to tolerate it is vital. As the poet John Keats said, to be a Man of Achievement (and I don't think that's a restrictive use of Man), you must have 'Negative Capability, that is, when a man is capable of being in uncertainties, mysteries, doubts, without any irritable reaching after fact and reason'.
I was brought up in a family of atheists the third generation of atheists in fact and for most of my life was an atheist. The period when I had to re-examine the received ideas of my atheist family, and those of the largely atheist social circles I move in, was one of the most uncomfortable periods of my life. I had a bad case of cognitive dissonance: my existing ideas no longer matched reality, no longer described the world adequately.
For me, Christianity is a theory in the sense that Evolution by means of Natural Selection was a theory for Darwin: the explanation which most simply and elegantly explains observed phenomena, even though evidence for some of its propositions is lacking. It is not that I do not have doubts and questions, do not experience uncertainty and mystery -- I do. But I am more capable of remaining in them now. I hope I have learned something about how it feels to be changed by views that are different from my own, and to see that process as valuable, not fearful.