This is a great thread. I think it underlines two things for me:
1) They are so scared of having doubts that they do not want to hear your reasons for leaving for fear that you will destroy their tenuous faith. I would suggest that if someone's faith is that fragile then they should seriously reexamine it (didn't we get loadsof watchtowers about examining our faith.....)
2) They have no real love. Unconditional Love would cause empathy; empathy would cause them to want to understand your perspective and your reasons for your position.
There is a concept called cognitive dissonance, it is where you have an uncomfortable feeling caused by holding two contradictory ideas simultaneously. I would suggest that these two ideas are 1) Watchtower teachings are bullshit and 2) if I don't keep to the teachings I won't get through armagheddon.
The only way to go back to feeling comfortable is to remove the dissonance, or contradiction. The only way for the sheep to do this is to blank out the belief of point 1, no matter what evidence they see to the contrary. The easiest way to do this is to ignore or distance themselves from any evidence that it is all rubbish, why do you think that there are so many articles in the literature about not questioning the teachings? If you question the teachings then you create dissonance as you uncover more evidence of point 1, which often leads to a removal of dissonance by stopping your belief in point 2, the road to freedom.