I think that this becomes one of the most central issues of the novel. I tend to see Changez as being reluctant about fundamentalism because he has embraced it as a response than as a statement.  Part of the reason why Changez is a reluctant fundamentalist is based on his own experience.  He has embraced fundamentalism because of his perceived rejection from America.  He is reminiscent of the jilted lover who seeks a "rebound."  Changez is more driven by his rejection from America than any tenet of fundamentalism.  It is for this reason he can be seen as reluctant.  Changez's personality is one that searches for some type of belonging.  He seeks to be embraced in some form of thought.  He strives for an intellectual and spiritual home where he can feel accepted.  He sought all of these from America.  The nostalgia that America undergoes and seeks to embrace in the period following the September 11 attacks cause him to be rejected.  It is this sting of rejection that drives Changez to seek sanctuary in the teachings of fundamentalism.  In this, Changez is a "reluctant" fundamentalist.  He is not a full fledged believer.  Rather, he is someone who has embraced fundamentalism as a way to blunt the rejection he experienced from American society.