I swear I wanna deck the producer of this movie. Throw out the book?!

The book is cannon! It came
before the movie.
Just to save you a small bit of ribbing in the future - the word you want is probably "
canon".
To me: Which came first is not important. Canon is not important. Being true to the original is not particularly important.
Why? Because if I wanted the same thing as the book, I could
reread the book, and have it be exactly canon and true to the original work. It'd save me the ticket money, and I can make cheaper and better popcorn at home. Even today, Hollywood cannot match my own imagination in terms of special effects, acting, or casting. The only reason I have to see a movie (or TV) adaptation of a book or comic is to see what is
different from the original, but still good.
The folks who do Shakespeare understand this - each retelling is a little bit different, and that's the point. To find the things that you can change a little bit, to give a different spin or meaning to the work. Small variations, or things you can do better than anyone else did before you.
This goes double when you change the medium in the retelling - what works well in a series of novels does not necessarily work in a novella, or a graphic novel, or a TV series, or a movie. And times change, so that audiences change - what spoke to people in the 1980s does not necessarily speak the same way to people of the 2000s.
V for Vendetta is a good example of this. It differs from the original work, but is (imho) still an excellent movie. Taken on it's own merits, without reading the original, I love it - I know this because I saw the movie before I read the comic. In some ways, I think the movie is better - Hugo Weaving's body language and ability to act
without seeing his face got some things across that weren't possible in the still frames of the comic.
Anyway, that's my own take on it. Each of us goes to movies for different reasons, so YMMV.