They then go on for four or so pages explaining why. I'm not going to summarize those here. If you are really interested, I suggest either buying the book (the link above goes directly to the publisher and I don't get a commission) or checking it out of your local library (if they don't have it, you can use interlibrary loan).
I'm not sure how convinced I am by their arguments. Maybe that's why I'm not going to summarize them?