Case in point: I've lived in UK for 8 years now, fully legally as an EU citizen. On paper, I should be able to apply for British citizenship tomorrow and get it without any issues. But I can't, because the Home Office completely disregards EU directive on the freedom of movement and the right to settlement - and yes, I have spoken to many immigration lawyers in the UK about it and they all say that Home Office is breaking the law in this specific case. There even is a case going on against the Home Office in the ECJ - but in the meantime, the reality of the situation is that I can't get a citizenship despite calling this country my home, paying all my taxes and being a law-abiding citizen with 8 years of residence here under my belt. Does that mean that my rights should not be protected, just because I don't have a British passport in my pocket?
I'm sure it works exactly the same way in reverse - there are British people who lived in Netherlands, Spain or elesewhere in EU for years, but for many many different reasons they can't become naturalized, because rules are what they are. Doesn't mean we should be suddenly stripping them of the rights they have been able to have for decades. Telling people to "just get naturalised" is not the solution.