I don't think any JW is without Cognitive Dissonance, unless they really have no thinking ability whatsoever.
So, once their beliefs are challenged, what is their first reaction ?
Nearly always, in common with others who have Cog. Diss, they challenge the integrity of the one offering the challenge they " Shoot the Messenger".
For example, the Alcoholic or heavy Drinker, when confronted with what may happen healthwise, will challenge the integrity of the research. The JW will do the same "Where did you get this information ?".
It is a device so that they do not have to actually examine the evidence itself, and hence deal with it. Why do they resort to this ? because of fear that they might find out the Truth.
What we need to be prepared to do whenever we are "anti-witnessing" is to spike their guns by saying something along the lines of "If something is true it doesn't matter where you got that from".
It is difficult though, I have had lapsed JW's of many years refuse to look at the excellent JWfacts.com site because they say it is "an Apostate site".
Well of course it is , from a WT point of view, but that is the only kind of place they will be able to get information from that will challenge their belief.
What it all comes down to is this, their faith is so weak that it will not stand any challenge or scrutiny.
How different from real Truth, which withstands any scrutiny.