The newly elected post-communist democratic Polish legislature could not reasonably be accused of running their country into the ground. Yet brain drain following the fall of the Iron Curtain was (and is) a real problem because it harms the country in a very real way. Eastern Europe is still paying for decades of autocratic communist rule, and looser border restrictions are certainly one contributing factor to the brain drain that continues to harm Eastern European countries (which leads to continued brain drain, which leads to a worse performing economy… you get the gist). There’s a reason the USSR forbid essentially all migration from East to West across the Iron Curtain.

From an individual perspective moving to a richer country makes sense, I’d do the same, but from a macroeconomic perspective this traps less developed nations in a vicious circle of brain drain leading to less economic development leading to brain drain (and more develpped nations in a vicious circle of de-industrialization).

I do not claim that this means that we should close down borders, as I still value individual freedoms quite highly and am generally pro-EU, but that should not prevent us from recognizing the very concrete downsides of those policies as well.