I agreeI think people are concerned about losing control of UK law and our ability to govern ourselves. I don't think people want to be part of a USA type of arrangement which is creeping up on them without any say.
Importantly, I think people perceive the EU as a failing enterprise with massive problems looming, most of which are being swept under the carpet. There are many failing economies within the EU and people fear that the UK will be forced into bankrolling them to keep the EU dream alive. We coughed up in the region of £1 billion to prop up Greece and we have "Greece 2" in the making along with Itally and Portugal and Spain and.... This is a concern.
This is based on talking to the people that I work with and talk to. Maybe we keep different company if all of yours were migration based.
For me it is not about imagration, but accept for some this is worrying, they see the impact in housing, social support, Health care. It is not racism
It is not about the economic arguements, because who can prove one way or another what will be in 10 years
But I agree the EU is a failing project, sinking, wrotten to the core, undemocratic, burecratic, and will drag this country down with it. That is what most people suspect, even if they cannot pinpoint it. In which case take back control becomes the rational conclusion.