Many people do come out of the WTS, so the mind control certainly is by no means 100% effective.
That said, I'm always amazed by how JWs who accept the "no one's perfect" defense for the GB at the same time believe that to question them is to rebel against Jehovah because He speaks through them.
Does He speak through them or are they just men? If just men, then why can't they be questioned? Doesn't the scripture tell us to "test all things"?