Criticizing a book fairly is one of the reader’s obligation toward the author. As the author was, throughout the book, trying to convince us with his/her arguments, we should pay him the respect by, at least, questionning these. In that sense, reading is like having a conversation with the author.
When criticiticizing:
Read not to contradict and confute, nor to believe and take for granted, nor to find talk and discourse, but to weigh and consider.
Teachability (the art of being taught), is key for understanding and make de book your own. This is why we must know how to critic a book. And there’s no book so good that it can’t be criticized, just like there’s no book so bad that we can’t learn from.
From: How To Read A Book, The Classic Guide To Intelligent Reading - Mortimer J. Adler, Charles Van Doren