If history teaches us anything at all, it's that the majority is irrelevant against an organised minority holding the real power.
I'm not sure what rate of expansion was intended at the formation of the EEC and I doubt anyone else does, or even that the EU was a vision at those early stages, but we know they went for quantity over quality, possibly believing that large numbers of mostly uninformed and economically dependent voters is the easiest route to victory.The EU has expanded far more and far quicker than originally intended. I believe that was largely due to UK and US influence...trying to turn Eastern bloc into Western bloc to capitalise on the break-up of the Soviet Union. It caused friction within the EU and the UK was very much to blame...to the point a backlash was inevitable.
Perhaps those that had visions of union based them on the status quo not changing quite so dramatically, and did not bank on new stuff like the www and other technological advances making information so readily available to the masses.
But it makes little difference if the EEC was a bait and switch or the switch was conceived later, because the European Empire is not what people want so soon after other failed Empires fragmented and folded.