Re: "With the lowest unemployment rate in decades?"
"That would be most countries."
Actually, it isn't. The troubles come from a small set of countries - just one is big enough to be able to create real issues if it fails, since it is in the Euro. It is true France could become an issue too as it let its debt increase too much. Germany had to cope with reunification in the past. Still most EU countries has a debt which is inferior to the UK one.
But as you pointed out, people still move (yet, if unemployment is low, where's the problem? It looks they fill jobs that will be unfilled, otherwise) because a simple index won't tell you everything about a country situation - as you tried to do in your original post.
UK had people going to work in Germany in the '70s. Especially when it destroyed too much of its manufacturing sector, being unable to keep it competitive like Germany did (and even Italy: https://ec.europa.eu/eurostat/statistics-explained/index.php/Industrial_production_statistics - which explains why Italy is somehow still afloat).
UK bet on the financial sector - but it concentrated UK wealth (not EU wealth) into a narrower share of the population - ironically mostly that Great London area which voted to stay, while in Northern England the situation doesn't look so good. And more companies could move manufacturing plants away, worsening the situation.
Attracting foreign wealth is of little use, if it doesn't "trickle down" to a larger share of the population - someone building companies that creates job should be welcome (as long as they also pay taxes too, as employees taxes alone won't be enough to run a welfare state), those just stashing money stolen from their own countries into bank safes while moving them from Panama to Jersey just make a few people in London richer (and again the money will be hidden somewhere...). You can't think that what works for Montecarlo, Cayman or Jersey could work for a sixty million people country.
It will be interesting to see what will happen once Brexit happens, and those who voted for it will discover it will bring advantages to the same "elites" they hated, and they will still get the breadcrumbs only - exchanging Polish neighbors with Indian ones...
Biting the hand that feeds IT
