Because only ex JW's can possibly expose what really goes on. Forget their use of biblical scripture to back up how they treat the disfelloshipped and what constitutes an apostate. Look at it pragmatically. It is very practical for them to demonize the biggest threat to their numbers and growth.
Is it in their best interests for the rank and file to talk to me or A@G, former Gilead grads who know the bullshit? To talk to Ray Franz? Randy Watters? Barbara Anderson? The Governing Body knows exactly what would happen, they would be exposed.
Thus, the flock is trained to hate apostates and exJW's. It's not for the protection of the congregation, its for the protection of the Governing Body.