As Freud pointed out, there is a compulsion to repeat those traumatic events that were passively experienced in an effort to gain mastery over them. People line up to see [horror films] in order to reencounter powerful unconscious anxieties while retaining a sense that they have some control of an active nature the second time around. Moreover, the movie provides an aesthetic distance so that the audience knows that the terror on the screen is not actually happening to them, and they can experience relief along with their fright.
Glen and Krin Gabbard, Psychiatry and the Cinema