I don't think all of them think that the F&DS is God's infallible channel. At one point, as early Bible Studies or children, yes, but after years and starting to see things as they are, not so much.
I think the fundamental flaw is not in the organization itself, but rather, in people's desire "to be right", to be "the only ones with the truth", to "feel special, be special" compared to others.
This fundamental flaw not only makes the Jehovah's Witnesses religion work, but Mormons, Muslims, and many other faiths as well.
That, coupled with a life vested in belief, makes changing difficult even when confronted with compelling contrary evidence. This leads to defending instead of changing.