Just like in most other European countries, France lets you say what you want, as long as you don't spread lies or hatred.
For instance, my understanding is that, in France, one should think twice before using the words "Mugabe" and "despot" in the same sentence. This is not a problem in the UK or the US at all.
But maybe this is also part of what made France such a very civilised, cultured and enjoyable place to live.
Can a French person say "The president is illiterate.", as Americans have often said about their president? Could they say "The idiotic president keeps on making up words."? Harsh criticism is naturally insulting.