An illustration came to mind.
We know that the society often talks about the need to "eat healthy spiritual food"
But imagine that we are speaking of literal food. We know we need to eat from all food groups, and consume the right items in order to be healthy. We should not limit our intake from just one source or one food group.
So imagine if you were told from an early age that the ONLY source of food was Macdonalds? True, you might eat a variety of items from their whole menu, but it is still all their food.
What if you were told there were no other sources of food? (No grocery stores, no farms, no restaurants, no markets) Worse still, if you learned of other places, you were consistently told that food from those places was "poisonous, bad or unhealthy"?
So too with the society! They tell witnesses that they alone are the source of "true spiritual food". No other sources of knowledge are acceptable or appropriate. In fact all others are BAD, and that even enquiring about them is punishable...
What a sad situation!