This is a great thread. The Brexit arguments sound hauntingly like the voices of the British American Colonists who wanted the King to phukk off, don't they? You can almost hear loyalist colonists expressing their dismay that these backward trash colonies would be cast adrift from home for good. Put in those terms, I can't say for sure I wouldn't have been a loyalist in those days.
Still, imagine any current US state (yes, including the State-On-Fire we call California that often boasts of being powerful) deciding to go its own way. It couldn't possibly be successful. As the world has shrunk, there are only several economies that rule the planet, including the EU. Without at least economic federation, are you sure individual EU countries wouldn't ultimately become feudal states in the service of China, the US, or perhaps Russia as Vlad poisons and treacheries his way to expansion?
In the case of the UK, setting apart the ripening internal discord, which way will you be pulled when Brexit becomes real? Will you feel compelled into closer alignment with the US? Strange to become a colony of a once-colony yes? Your economy will be non-competitive on its own even before you lose Scotch money and have to tangle with the Irish again. What will become of you? Is it better to be proud, loudly British, but dirt poor and vulnerable, or is it better to remain aligned and with a roof over your head, with compromises required along the way?
I get the arguments about control and cultural identity, which will necessarily diminish as the EU matures, and someone fiercely British, or Polish, or German could be forgiven for their angst about the future for their progeny. If it makes you feel any better, Americans can all agree that southerners are trash and that New Yorkers are ugly and obnoxious, so it's possible to retain some regional 'flavor' even as you become citizens of the light blue EU monolith.
Besides, we're all going to wind up under some Star Fleet World Bureaucracy in the future aren't we?