HayFeverHell - like the name - fellow sufferer - could barely see yesterday!!
"No one can have their cake and eat it too." - I think that is key to how many people feel.
(I know that this was not your point HayFeverHell - I don't want to put words inot your mouth - this is what I have observed in my own social circle and what I meant by "double the advantages".)
Non-British Eu residents want two citizenships, (handy if it all goes tits up) - I can have only one.
Mrs Bloggs pays London costs of living out of her child benefit whereas Mr Non-Brit who is working here but bringing up his childern in much lower cost EU country claims the same and has it sent home where it is worth a lot more.
Family X claim housing benefit while owning a flat in Prague and renting it out while living in the UK. (Yet rules for foreigners, (ie Brits), buying second homes in Prague and other cities in EU countries make it impossible for them to do the same)
In the UK full language support, financial help and general acceptance, (especially in the major cities), make the UK a great place for EU migrants. That is not reciprocated. If Ms Bloggs pitched up with her three kids in many EU cities with her kids - the opportunities and support would not be there.
I also agree that many EU people , (not just in the UK - talk to the Spanish about this, or many of the French and Germans) feel that:--
"this is one of the shrinking areas that really is about citizenship of the nation-state"