The Act further clarifies that
For the purposes of this Act, goods are of satisfactory quality if they meet the standard that a reasonable person would regard as satisfactory, taking account of any description of the goods, the price (if relevant) and all the other relevant circumstances.
When you buy the book, you're doing so because you have an expectation the story will be entertaining, or having it available is somehow useful to you.
Unless you have been lied to, by the bookseller, the fact that your expectation does not match what happened is not the problem of the seller of the book. Moreover, especially when you physically purchase the book from a brick-and-mortar shop yourself, unless the book has never been opened or read by anybody, you have had ample opportunity to check whether the book is of suitable quality for your purpose, as a reasonable person would do.
As a consumer you are protected from books being printed on tissue and bound with spider webs (durable), with invisible ink (fit for purpose), covered with razor blades (safe), and generally not tatty (suitable appearance and finish; freedom from minor defect).
As such, there is no conflict between consumer protection and free expression. You are assured a book you can read for a long time, and should you dislike the story, you're also free to burn it (subject to pollution and hazard laws).