Where did the phrase "chopped liver" originate?
Why does it mean "of little value"?
According to the Phrase Finder, chopped liver is always served as a side dish, never as a main dish. It therefore makes a good metaphor for someone who's being treated as unimportant or dispensable.
Wikipedia has a page for Chopped Liver, which also explains the origin of it as an expression.
Since eating chopped liver may not be appreciated by everyone, the Jewish English expression "What am I, chopped liver?", signifies frustration or anger at being ignored on a social level.
An alternative explanation for the etymology of the "What am I, chopped liver?" expression is that chopped liver was traditionally served as a side dish rather than a main course. The phrase, therefore may have originally meant to express a feeling of being overlooked, as a "side dish."
A similar reference aired in 1963 on The Dick Van Dyke Show on an episode titled "Jilting the Jilter" at the Internet Movie Database. Sally Rogers, played by Rose Marie, is asked by a "second-rate comedian" Fred White, played by Guy Marks, "What do you think you are your majesty, chopped chicken liver?"
I have always understood the analogy to be a culinary parallel.
On the one hand, pâté de foie gras is made from the finely pureed livers of specially fattened geese or ducks. Its composition is governed strictly by French law. It is a prized and expensive luxury food item.
Unlike pâté de foie, mere chicken livers have no place in the culinary pantheon of food fit for the gods, e.g., truffles, caviar, etc. They are coarsely chopped, rather than pureed. They can be tough and chewy rather than melting on the palate. Many Americans would regard them as mere offal, more fit to be fed to the family dog or cat rather than being served at the table. At most they might be chopped fine and used to flavor a stuffing or a gravy rather than being savored on their own.
The heart of the protest, "So what am I, chopped liver?" focuses on the fact that two persons are treated in markedly different ways for exactly the same accomplishments, even though their essential character and/or actions may be substantively identical. After all, there is no inherent difference between the functionality of a goose liver, duck liver, and a chicken liver.