The parsnip has served humanity honorably. It's brightened many a dish of salt cod, perfumed many a stew and stock, been made into many a pie (Martha Washington's personal cookbook included a parsnip pie). Boiled parsnips with butter were once so common that they gave rise to the proverb, "Fine words butter no parsnips."
But this relative of the carrot just can't get respect. It has often lacked a name of its own; the Latin pastinaca meant either carrot or parsnip. The Arabs had no word for parsnip, so when they came to Spain (where pastinaca had come to be pronounced something like pasnar), they adopted the word, mangling it into sefennariya. The Spaniards then borrowed the word back, mangling it even more into zanahoria--but then that became the Spanish word for carrot. (English insulted the parsnip further by suffixing the word neep, meaning turnip, to pastinaca.)
Certainly, the parsnip is homely--scrawny and pallid yellow, like a carrot recovering from a bad flu. And despite its real virtues, there have always been people who disliked its sweet, spicy flavor.
In the 18th and 19th centuries, the potato started to displace it in many European countries. The nadir of its reputation was early in this century. The current edition of "Larousse Gastronomique" at least mentions that it can be cooked like carrots or kohlrabi, but the 1920 edition said parsnip was strictly for flavoring pot au feu . . . or feeding to livestock.