I wouldn't offer western Europe as an exemplar of thriving Christianity. You'd have to go to Africa, Asia and parts of the Americas for that. China numerically became the largest Christian country on the planet a few years ago.Ok so surely its better to have European immigration (Christian countries) than from the rest of the world.
I think people will have a shock if some of what the leave advocates say is true. If, as they say, we should choose the skills we need from all over the world there is likely to be much less integration with new immigrants.
I won't speak for everyone but I personally find I have more in common with Europeans than Americans when it comes to values and my beliefs about the world. Even language which is one of the main barriers to European integration is a lot closer to English than a good majority of non European countries.
Can you honestly tell me, for example, that we have more in common with most commonwealth countries than France.
I'm not anti-European, I spend lots of time in European countries. I am suspicious of the end game of the EU project and its influence on the cultures of its constituent nations.