I had an elder Friend who had a Koran, just to find faults in it and argue that with the Muslims.
That same elder Harassed me for reading "Crisis of Conscience".
There is great fear of apostate information. A person is unlikely to become a Muslim or Mormon after reading their holy books, but there is a far higher likelihood of them leaving the religion after reading apostate information. It is all about damage control.
I wonder how Maclean would square having other religions' publications sent to you with the strong admonition of not accepting other religions' literature at the door. Sometimes people will say 'I'll take your Watchtower if you will take my literature,' and we were always told to never take it.
There is quite a lot of variance on this topic. Research everything, be like the Boreans, make sure of all things, but don't spend too much time looking into information not actually provided by Watchtower - a typical form of information control.
One of the reasons that we were not to take literature from a householder was so as not to give the impression that their information was of the same value.