The EU was never comparable to, say, America in terms of unity. Europe had too much history for it to work perfectly - every one was on what had been at some point some one else's land.
[0] https://europedirectemn.files.wordpress.com/2018/02/treaties...
You could say that about the UK - which lost a significant chunk last century and could well lose rather more this century.
Example https://www.tsb.co.uk/current-accounts/faqs/identity/
At what age do you become eligible for the electoral roll? At least in the states most people register to vote before they leave the house of their parents.
Generic and incorrect statement
Also, I'm not an UK citizen and I'm forced to give up my biometrics (face) whenever flying out of an UK airport. Or when flying into the US.