Funny you don't consider it dictatorial to join the EU on a presidential mandate, but it is to leave it.
Which president unilateraly decided to join the EU please? In which country?
I have no clue what you are refering to.
In france the Maastricht traitee has been signed by the senate and the conseil constitutionnel. It wasn't the single decision of the executive.
It also has been accepted by referendum in 1992 by 51.04% of the votes.