By contrast, Finkelstein adopts an ugly conspiratorial tone when he attributes the book's popularity in the United States to its Zionist message.
Finkelstein doesn't consider the possible Zionist message in the book. 
mnli hypothesis: Finkelstein doesn't consider the possible Zionist message in the book.  premise: By contrast, Finkelstein adopts an ugly conspiratorial tone when he attributes the book's popularity in the United States to its Zionist message.