In my hall, there were several ladies that were intelligent and had world experience. But the thing is, if a witness comes to your door with a sincere and honest personality, you could make the assumption that what they are saying is also sincere and true. None of the ladies were hypocrites or mean and often had interesting well thought out comments. They were not raised in the "truth". But once you start building on the assumption - if they are honest, then the ones leading them are honest too, then you might ignore other signs that all is not right.
I used to think after reading how terrible it would be to take God's name in vain or use God for unscrupulous means, they would never do this (the GB) because they would lose all hope of everlasting life. If you were to suggest that this isn't so, I wouldn't have believed you.
There is also those who have experienced or seen terrible things in other religions. Maybe JW's from this view, seem a whole lot better.
Anyway, once you have assumed that this is the only truth, you no longer look. That makes you "dumb" even if you are smart.