France likes to think of itself still as a major world power. Unlike every other country in Europe they still have an empire, ok, it's just a few islands in the carribean and Paciffic, but.hey, they can still vote in French elections, pay French taxes, use the Euro and the French Telephone system. (I am not making this up), even the new Euro notes that have a map of the EU on them have little boxes with maps of various islands in them. You would never think that Martinique is in Europe, but it is.
France never really got over the post was independance thing, and thins hang up about it's shrinking world influence is reflected in it's desire to have a language that is an international currency, with it's own distinct identity. The Acamdemie Francaise exists to make sure that the language itself is maintained and that there is a defined way of speaking it.
By historical accident English is the language of international currency and this is unlikely to change. If it does it will be to something like Spanish or Cantonese.
So if I was French I would probably be a bit miffed if someone unapologetically addressed me in English and expeted me to answer back in that language.
Interestingly other countries in Europe especially Holland and the Scandics are far more comfortable being multi-ligual