Excerpts from The Monster Show by David J. Skal (thanks for loaning it, Jen):

[On Rosemary's Baby, Alien, The Brood, etc.] The accumulated weight of birth-related horror imagery amounts to an undeclared war between the living and the unborn. There may be more to the matter than metaphor; the unconscious likely makes no distinction between geographical invasions and physical violations. Your body is a battleground, a feminist slogan widely popularized in a postmodernist art poster by Barbara Kruger, is, not uncoincidentally, the subtext of innumerable horror-movie posters and paperback book covers.

...

[Tom] Savini told a magazine interviewer that "much of my work for Dawn of the Dead was like a series of portraits of what I had seen for real in Vietnam. Perhaps that was one way of working out that experience." Horror films of the seventies and eighties began exhibiting symptoms remarkably similar to some of those suffered by victims of posttraumatic stress syndrome: startle reactions, paranoia, endless scenes of guerrilla-like stalking, and, like traumatic flashbacks, endlessly repeated images of nightmare assaults on the human body, especially its sudden and explosive destruction.