To answer your questions

> Does brain drain not exist?

Of course, I've seen it within regions of the US. Imagine how insane it would be to say that NY city should resist hiring workers from NJ because it hurts small NJ towns. My experience is that the root cause of brain drain is the regional government, keeping talented individuals there only stifles the growth of those individuals, it doesn't improve the region. In fact we see this locally a lot, many more people do move back to NJ from NYC than do to PA from NYC since the former tends to have a lot more to offer returners than the latter.

> Do you want to exfiltrate the young generation from worse off countries?

Of course! From what I've seen either two paths are followed. When local governments have no plans to improve the country they lose all their talent and those individuals succeed. The other path is the China/India path, they improve their economies through exchange eventually become attractive and more youth return and newer generations are more likely to stay.

> Do you want to incentivize young workers to leave their native countries instead of whatever else you must think young workers can contribute there?

Absolutely! It's one of the reasons the US has been able to rise to the level of technological success it has. Most of our greatest scientists where fleeing countries in decay. My experience both locally and globally is that talent staying in an area that is in decline only hurts the talent. Typically it is the governments of failing countries that try to halt immigration out first.

> Do you want to signal to the local young workers they are wrong in refusing the local salaries because someone from abroad will take them?

Yes! I've worked in poor US towns and I always encouraged the best and brightest students to go to a major metro area, expand their skills and get paid more. Would you not encourage a brilliant student from an area of the UK in decline to head off to London to further their career? If the poor town shows improvement they can return and improve the town and live with their families, if the town does not improve then they at least don't waste their skills.

> Do you want to signal to the local population that there's no incentive in raising the next generation because the solution is to have people born and educated abroad to come here to work temporarily and then abandon (with their savings, I assume) the country once they had enough?

I'm not sure the logic of this question. Again, I live in the US where nearly the entire population has their origins in immigration at one point in time. We've never had a challenge with raising the next generation while being open to immigration. Our biggest problem is not immigrants coming in, but jobs going out (as far as manufacturing goes). Your critique of "abandonment" also doesn't make sense given your earlier points. I have plenty of Chinese friends who have stayed in the US and start the path to citizenship and plenty who have gone back to take leading roles in Chinese companies. I consider both of these paths to be a net win.

> Do want to continue to degrade the social fabric by insisting in economic advancement instead of fixing what leads to lack of workers?

I think by definition nobody wants to "degrade the social fabric", and I'm not sure what you mean by this? Do you mean you don't want foreign people mixing with your locals? Again, as an American my experience is that diverse ethnic influence is precisely what makes communities stronger. One of the favorite parts of my neighborhood is the Polish butcher (I have no Polish background), I love being able to go to a Chinese neighborhood and not hear a word of English for an entire afternoon.

Can you point to a single example of a country that has halted immigration and "fixed what leads to a lack of workers?"

It seems like the UK is experimenting with tighter controls but from what I've witnessed it's not going great.