Well, of course, Invasion of the Body Snatchers is classic H'wood allegory, and what I would imagine to be esp. valuable about it, in terms of class discussion, is, What is it an allegory of, exactly? Commie infiltration? Or social conformity?
A lot, A LOT, of horror is easily read as allegory. Romero is of course key- for Night of the Living Dead, civil rights, but it's also a critique of the family (return of the repressed, for Robin Wood), whereas Dawn can be read in terms of consumerism. I suppose critique and allegory begin to blur here, or more specifically allegory and metaphor. How would you specify that distinction? Consider, for instance, the original Cat People. Or, most/all Buffy episodes (eg., Angel loses his soul after sleeping w/ Buffy as allegory of women's fears about losing their virginity). Or, Rosemary's Baby- it's actually about pregnancy, but being impregnated by the devil makes it about fears surrounding pregnancy in a broad sense.
If this sort of stuff is allegorical on the lines you are thinking, then certainly you should look up Wood's stuff on horror, like the chapter in Hollywood from Vietnam to Reagan.
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