Name one country with better-than-average standard of living that has opened its borders and thrived. There will always be a wall around something nice — either around your house, or your neighborhood, or your country.
Even today, we have "open borders" within the US. People are free to move from from poor (or poorly run) communities to places with more opportunities and it's a win-win.
Similarly Europe has 26 countries in the Shengen area. Some of the countries have a "better-than-average standard of living" and they're doing just fine.
There was no welfare state back then, and the economic situation was vastly different. Also saying it went "quite well" looks over all of the ethnic tension that took decades to fix. https://en.wikipedia.org/wiki/Irish_Americans#Discrimination
> Similarly Europe has 26 countries in the Shengen area. Some of the countries have a "better-than-average standard of living" and they're doing just fine.
Heard about Brexit? The Romanians are coming: https://www.youtube.com/watch?v=Yb1AkaKJL08
The UK was never in the Schengen Area to begin with.