It is often maintained that the only thing worth writing about is "the human heart in conflict with itself", but I think accomplishment and building for the future are more worth writing about. These two themes are core themes of Science Fiction, making SF the most valuable literature of all. Indeed, building for the future is what we all do every day, except sometimes if we're on vacation, retired, or have given up on life. Building for the future is the most important activity, making SF the most important literature.
Also, of course, SF is "the literature of ideas".