I wonder how much of it is psychology at play. On the one hand, I knew a few people who worked at Bethel or visited regularly and had reasonably high-level access to the GB. These were people who struck me as 100% true believers who had no doubts about the WTS being the one true organization led by god.
And yet, learning years later about stuff that they knew, I can't fathom how they could be so loyal and faithful if they knew the things they knew. Were they really that good at deceiving everyone around them? I think they had deceived themselves, because I never got the impression (and in some cases, still do not) that they were being insincere.
Maybe it's a form of group psychosis- you aren't quite sure, but everyone around you seems to be convinced, therefore it must be true. And so you behave with full confidence, not realizing that you are helping to reinforce the delusion for other people when they had doubts. And no one wants to express their doubts, lest they draw unwanted attention!