In horror fiction, every culture has its own supernatural menace. African Americans get voodoo. The Chinese get fox spirits. And WASPs (white Anglo-Saxon Protestants) get the all-American boy sporting a varsity letter jacket and blinding-white smile that mask the howling maniac on the inside.
That's probably a leftover from the victorian era, where society was collectively obsessed with the idea that otherwise respectable facades were hiding dangerous and/sordid behavior. That gets explored in everything from Sherlock Holmes (most prominently in The Man with the Twisted Lip) and The Strange Case of Dr Jekyll and Mr Hyde to contemporary yellow journalism.
