"Chldren Of Men" -- The Book Vs Movie

I just watched director Alfonso Cuaron's very entertaining debut film -- "Solo Con Tu Pareja" -- on DVD last night, so I'm primed to see his new film "Children Of Men." I don't expect great things given the reviews that are all over the place, but it should be interesting. The NYTimes has a piece comparing the book by PD James to the film. I haven't read the piece closely since I haven't read the book OR seen the film and don't want to spoil either. But one passage caught my eye: writer Caryn James says "“The Children of Men” is not another of Ms. James’s famed detective novels, and it is not, as it has sometimes sloppily been described, science fiction." What is sloppy about calling it science-fiction? The book -- first published in 1992, I believe -- is set in the year 2021. The film seems to have pushed that forward to 2027. Everyone refers to the novel as a dystopian tale, which is certainly a form of sci-fi. How could any book set decades in the future be anything but science-fiction, regardless of its plot or conceits (even a romance set in the countryside would be sci-fi if the author tells us it is taking place in 2354, surely. And "Children of Men" is classic sci-fi in using a setting of the future to explore urgent issues of today. Does James think sci-fi is a banal, secondary genre? That would be bizarre, since she's discussing P.D. James, an author who has won acclaim for writing detective novels. I thought the days of dismissing sci-fi were long past, but I guess we'll have to wait till at least 2021 for that to happen.