From Vivian Carol Sobchack, The Limits of Infinity (A. S. Barnes & Co., 1980), pp. 29-30.
One major difference between the genres lies in their sphere of exploration, their emphasis. The horror film is primarily concerned with the individual in conflict with society or with some extension of himself, the SF film with society and its institutions in conflict with each other or with some alien other. Therefore, the arena for conflict in the horror film is usually as small as a minute town tucked in the Carpathians, an old castle, or an English village, while the arena for the SF film is most often the large city, the planet Earth itself. If one genre is as large as the human soul, the other is as large as the cosmos. Both genres deal with chaos, with the disruption of order, but the horror film deals with moral chaos, the disruption of natural order (assumed the be God’s order), and the threat to the harmony of hearth and home; the SF film, on the other hand, is concerned with social chaos, the disruption of the social order (manmade), and the threat to the harmony of civilized society going about its business