Perhaps because ever since childhood I've lived in and been 'at home' in quite a few countries I've never really understood flag-waving. Cheering for your sports team, your school, your friends - yes, of course. But the geographical location of that bit of the planet where you happen to be born, or where some of your ancestors were born, why is that such a big deal? Sometimes you want another country's team to win the football - why not? Does that make you a traitor?
The fear of immigration is the fear that we'll all get mixed together and the lines of demarcation will gradually become fainter and fainter. Would that be such a bad thing? Eventually the mix would produce new ideas, new people, new solutions. New problems too, of course, but that's life innit?