The curious thing about 'cognitive dissonace' (if it even exists, which Teary still debates with himself about), is that you can't really KNOW that you have it while you have it -- you can only know you had it or didn't have it in retrospect. It is like some quantum particles: once you realize that you have it you don't really have it anymore (or maybe it is like, if you know that you are crazy then you aren't really crazy). A Witness reading this thread might have CD about his current beleifs, but the OP of this thread might also have CD about his current set of beliefs and not even realize it.
The other thing to think about, is just how wide spread and common the phenomenon is. Is a rare thing that only effects this one tiny group of individuals that call themselves "Witnesses," or can it crop up in all kinds of places that we wouldn't normally associate CD with? What about normal churches, like Baptists or Lutherans? Are they somehow immune? What about atheists? Buddhists? Ex-Witnesses? If CD is merely discomfort because of "holding conflicting ideas simultaneously" caused by subconcious doubts about ones current set of ideas, then you would think that the theory could apply to just about all of humanity in every type of group and social construct.
Because remember also, CD says nothing about the truth or falsity of one's ideas -- it is more a feeling, or a value judgment, than it is a factual thing. A Protestant might experience CD because he subconciously feels his current set of beliefs are wrong and that Muslims beliefs are more logical, while a Muslim might experience CD because he subconciously feels that his current set of beliefs are wrong and that Protestant beliefs are more logical. So anybody anywhere could have CD so long as any doubt at all exists in their mind, regardless of whether those doubts are justified or not.