How do you deal with population density, optimal currency area issues, bankruptcy of countries who have working populations who migrate to here?
FYI the main reason I voted to leave is that the Eu isn’t congruent in its decision making (fiscal vs sociopolitical) between countries, plus the enforcement of northern European economic policy on Southern European policy leads to issues and mass migration to the places where said economic policy is in place.
The vast majority of people move because they have something lined up already. It's a peculiar notion that people will travel thousands of miles on the off chance that something good will happen. So if people have a job and somewhere to live, who's business is it but there's and their employers what's going on?
The government very much has to get better at providing funds for government-run services to adapt to changes in population, but this is true even if there were no international migration. Just this week, Sheffield Uni research highlighted the national inequality throughout Britain
and obviously one way around that is to encourage greater mobility of people. For instance, official figures from the ONS say that 42,000 Brits moved to Birmingham in 2014. No one grits their teeth and says how terrible that is, they just get on with it and try and adapt. If 42,000 Poles moved to Birmingham you'd perhaps get a different response.