How is Frankenstein's monster depicted as an anti-hero?

There are certainly ways in which one might argue that Frankenstein's monster lacks conventional heroic attributes.  In Mary Shelley's Frankenstein, Frankenstein's monster is willing to kill innocent people to exact revenge on his nemesis and creator, Victor Frankenstein. Killing William, a child (though kind of a poorly behaved one), and Justine, Henry, and Elizabeth, all innocent people, makes the monster seem more like an anti-hero.  Heroes are supposed to uphold the innocent and good and defend them from harm; the monster kills them to prove a point and isolate his creator because Frankenstein's monster believes he, the monster, has been forced to live in isolation due to his creator's decisions. Although the monster begins his life as a benevolent and good creature, and though he remains kind for a long time despite the terrible treatment he receives from everyone he encounters, the monster eventually chooses to live for revenge. Revenge that compels one to murder innocent people is never appropriate hero behavior.