A human is brain, five senses and a mechanism in form of a body. The senses and body depends on brain for their use. If a human uses them to learn things one should end up a decent rational human being, able to judge all else that he comes across from a 3rd party.
The 3rd party information is ok if it is rational because that is what knowledge is. If the 3rd party information is nonsense then it is not rational.
Some people are rational other irrational. The rational people look at information by way of logic and evidence but irrational people just take anything in any direction.
The quran is a rational book revealed by Allah to make people rational because that is what knowledge is all about. People who have not bothered develop their rational faculty, it is not possible for them to understand the quran.
To them whatever someone else tells them is the final word. On this basis they judge things and reach their conclusion.
Terry johns is also such an individual who has been told silly stories about the quran so he used them for making his decision about the quran. I blame us muslims for that because we have covered up the quran in to a lot of make beliefs and nonsense which are difficult even for us muslims to avoid never mind a nonmuslim.
It is time we discovered the quran ourselves and then helped people like terry johns. It is easy to blame others but overlook one's own mistakes.