As in Germany (which halted use of the word "Fraulein" in official forms and documents in 1972), and following earlier steps by French municipalities, the government of France has killed "mademoiselle" from official use. Women will be addressed as "Madam" regardless of their marital status, just as men regardless of marital status are addressed as "Monsieur."
This may sound quaint, but we've done much of the same in the US with the move toward "Ms."
For an explanation why, ask yourself what's wrong with living in a world with perfect purity of language, depicted so wonderfully by Douglas Hofstadter.
Remember: the only language that doesn't change is a dead language.