Should a book mention sources that are opposed to its thesis? That depends on what kind of book it is. If it just seeks to present a certain view, and makes no claim regarding the existence of other views, then it doesn't need to mention those opposing views. But certainly if a book is attempting to be any kind of definitive guide to the range of legitimate views, and there are views that are ostensibly legitimate and yet are outside of the range permitted by the book, then it should mention them, and account for them.