France is not a dictatorship. It's not like the president can just say that the country will be leaving the Union.
But it is ok if they do this to join the union right
It's not about joining or leaving. It's just not how it works
Edit: at least in France and most democracies which is a criteria to actually join the EU.
Funny you don't consider it dictatorial to join the EU on a presidential mandate, but it is to leave it.