A common motif in horror movies is the monster who is sexually attracted to, or even in love with, a normal. Usually the monster--or deformed destructive being (DDB)--is a male, and the normal a female. This was the case in both versions of The Fly, and in The Creature from the Black Lagoon, and in Psycho, in which Norman Bates's attraction to Marion Crane triggers his killing spree. But the archetypal version of this setup is found in the original King Kong (1933).
Kong, a giant gorilla, is deformed with respect to his size and destructive of life and property, qualifying him as a DDB. In addition, his love for the blonde Ann Darrow (Fay Wray) is destructive because it violates the rule against transspecies romances (with implicitly, perhaps, a racist fear of miscegenation). Biomechanically, the romance could never work--how could conventional vaginal intercourse ever take place? And Kong fails to win Ann's consent--this is why she is always screaming at him whenever he picks her up--making his advances tantamount to rape.
For all these reasons, Kong's love is wrong: the most fundamental sort of deformity and destructiveness. Yet a great deal of audience sympathy is worked up for Kong's love. He is tender with Ann, even when he strips off her clothes, in a mix of curiosity and randiness. He is protective, zealously fighting dinosaurs for her and breaking his chains when he thinks the photographers are attacking her with flash bulbs. He does prodigious feats for her--breaking through the monumental island gates; climbing the Empire State Building. Before he dies, he carefully puts her down so that she will be safe. Finally he dies for her. The idea that Kong's story is a modern-day "Beauty and the Beast" is played up throughout the film, and this is the strongest cue for audience sympathy: despite Kong's DDB status, he is to be understand as a fairy-tale hero, a star-crossed lover.
The combination of rampaging horror--embodied, above all, in the screams of the beloved--and the unrequited love that drives the agent of horror are what make Kong such a great film. Kong welds together two great passions--fear and love--and holds them together until the end. The failure of its remakes to do so (1976, 2005) is among the factors that makes those films weaker. In both of those films, particularly the 2005 version, the blonde feels affection, even love for Kong. Mistake. The blonde's love for Kong makes him less of a DDB, breaking the balance between fear and love. The first movie had it right: Kong picks up Ann, Ann screams, Kong is in love. And Ann keeps screaming.