Do you think there would be any benefit to explaining cognitive dissonance, confirmation bias, sunken cost fallacy etc prior or at least early on in a conversation like this to prepare them for the mind wanting to back out of the logic trail?
I would also explain what the Mormons etc that are discovering their religion is not what they think it is are experiencing when they start to investigate.
Here is a great link to share, IMO, with someone willing to look at the WTBTS as possibly being wrong. It is the story of a Mormon thinking his way out of his religion and he uses the jws as a proxy religion so that he could remain somewhat unbiased.
http://www.youtube.com/playlist?list=PL5F1EB3B4F919226D
NJY