Cognitive dissonance is uncomfortable. One way to alleviate it is for everybody around you to believe the same thing. This social reassurance of the impossible things you believe relieves much of the discomfort. This is why people in cults feel such a need to exclusively associate with members of the cult and convert everyone they meet. Not only that, but constantly trying to convert is an unconscious method of reciting the impossible belief until - like a word said over and over - it begins to lose its real meaning and just becomes rote. Rather than having to be dealt with on an intellectual level, it becomes like a nursery rhyme that we know the words to and can sing, but we have never stopped to think about what the words actually mean. Some are pretty horrible, when you examine what's being said.
I did notice he quit arguing with me about Nisan 14 vs. Nisan 15. The Society just throws it out there with a few blurbs from minority theorists. The fact that it's easily demonstrated that JWs are incorrect made him very uncomfortable talking about it, once he realized the cause was clearly lost and the Society is obviously wrong. The 607/587 thing is much murkier. The Society has fought tooth-and-nail for this, has turned over every rock for any nutter's parallel opinion, and flooded the literature with enough words to make it virtually impossible to tear down the arguments of anyone who wants the Society to be right about it.
Once someone puts the "teacher" hat on, it's very difficult to reason with them. I've tried it with JWs and Mormons who come to my door, fundies, JW family and acquaintances (there are no real JW friends), etc. It doesn't work, because you can lead a horse to water, but you can't make it drink. Someone has to want to know the truth in order for the truth to be given to them. It takes a lot of will power to admit you're wrong and certain types of people would rather die than change their minds. The more you fight with them and back them into a corner, the more tightly they cling to their beliefs.
The psychological reasons for clinging to lies are as strong or stronger than clinging to them for money or power. It's my experience that many (or most) JWs have some kind of mental issue. Some have low self-esteem and crave the feeling of "success" and the false love and praise for toeing the cult line. Others are sociopaths who crave the man-made positions of authority and/or the superiority of believing they're in a tiny minority who will watch everybody else die at the hand of God for not listening to them.
Once you realize most JWs don't have rational reasons for adhering to the JW doctrines, it's easier to let go of an argument. It's impossible to reason with someone who is being unreasonable. Their belief is on a purely emotional level, so the only thing that will jar them loose of their death-grip on the group is an emotional event. Most ex-JWs are made by something traumatic happening to them; not a realization through study that "The Truth"™ isn't very truthful, at times. You just have to wait until they're thirsty, then lead them to the water. Eggie is obviously not stupid, but all that does is make him better at making intelligent arguments for beliefs he clings to for stupid, irrational, or possibly wicked reasons.
