My girlfriend is French and she, along with her family, despise peanut butter. It makes me laugh! They say its 'too fat', and they don't like the taste. To each their own I guess.
It's just not commonly part of the French diet, and since it's got a very pronounced flavor it makes for really unusual combinations to a French palate. Like most things, it's an acquired taste. (I'm French and peanut butter is okay with me.)