The Horror, The Horror

I was recently watching the 1972 film version of Kurt Vonnegut's Slaughterhouse-Five. No classic, but it's an intelligent, reasonably well-made film from director George Roy Hill.

It's probably Vonnegut's best work, and was the bestseller than made him a superstar novelist. It follows protagonist Billy Pilgrim through his days as a prisoner of war in WWII who witnesses the bombing of Dresden (just as Vonnegut did--he even makes a short appearance in the novel). We follow Billy's post-war life, but the twist that makes people think of it as sci-fi is that Billy is (or believes he is) taken to the planet Tralfamadore, and becomes unstuck in time, no longer living his life in chronological order.

The movie captures much of the story--the tension, the tragedy, the humor, the time shifts, etc. So I was surprised, when I hit the info button on my remote, that the genre of the film was "horror." It may be a lot of things, but horror? Who's in charge of these categorizations?