"Their faith is so fragile that they could be swayed in their beliefs by merely associating with someone who has a different viewpoint."
I think this statement sums up the reason the WTS doesn't want thier followers asociating with anyone that doesn't believe what the WTS dishes out.
One question all JWS should ask themselves is,
If the WTS has and teaches the 'truth', then it SHOULD and CAN stand against any acusation, inquiry or attack.
So why should I be afraid to face unbelievers in the WTS?
Why?
Because the WTS tell them that they must not asociate with any that question the WTS.
Because the WTS knows that there are many teachings that would NOT stand if put under a magnifying glass.
neyank