NickM said:
Well, that depends. If, having finished the book, he renounces his pernicious belief, he's open minded. If he doesn't, he isn't.
That doesn't follow at all. Certainly he could do that, but
not doing so does not automatically mean that he's not open minded. He may find that there are elements of the book's argument he finds to be flawed or unacceptable. You seem to be suggesting that he accept the book's thesis without critical thought, which seems a little silly.
Let's reverse your argument to see how:
'If, having read the Bible*, you immediately renounce your wicked ways and become a Christian**, you're open minded. If you don't, you're not.' Have I got that right?
*...or Koran, or Torah, or Guru Granth Sahib, or...
**...Muslim/Jew/Sikh/etc