When I read the article (haven't read the book) I came to think about two things in terms of explanations: For one, academia is a rough place. Competition about grants, positions and power is high. The battle between different methodological and theoretical schools can be fierce. I haven't heard about anonymous 30 page angry letters before, but I wouldn't say it would surprise me at this point.
The other thing could be rooted in denial. If someone presents a reality that you don't want to be a reality you could either accept it and the consequences (political for example) that comes with it, or you can deny it and try to find the faults within the description, making it void.