The usual function of the "revenge flick" is to allow the viewer to vicariously experience the brutal pleasure of executing that "dish best served cold." It's a basic case of good versus evil, with the former striking back against the latter. These films are typically not intellectual; they are visceral and work on a base level. Countless examples can be found in Hollywood but perhaps the most infamous is Death Wish. The 1974 Charles Bronson movie became the template for revenge flicks to follow. Leave it to Neil Jordan to turn the genre on its ear.
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