This is the worst case scenario for immigration but in reality it doesn't work like that. People do return to their home countries at some point in their life not all of them but some of them and it's very documented and they bring invaluable expertise and much needed capital know-how with them. Also, not all migrants are unskilled/low skilled labor, some are very high skilled and can benefit the host country enormously whether directly in taxes or indirectly as rising productivity and national wealth as a whole.

Yes, the expertise brought back is invaluable, indeed.

The general consensus is, I believe, that immigration has negative short-term effects on wages for low-paid workers or people just starting their careers, but eventually leads to economic growth due to higher demand. Some countries even rely upon immigrants to keep their social security system up and running, due to their own citizens aging rapidly and not having enough population growth. I believe Germany is one such example.

For the countries currently losing most of their qualified and educated citizens, it's certainly not a good thing.

I think this is correct, but I'm having trouble finding proper peer reviewed publications on the subject. The search is very noisey for obvious reasons.

Here's someone who says that immigration contributed moderately to the rise of wage inequality by increasing the supply of low-skilled labor during the 1980's, but that the effect on native worker outcomes was very slight: http://www.jstor.org/stable/2118131?seq=1#page_scan_tab_cont...

EDIT:

"Some countries even rely upon immigrants to keep their social security system up and running, due to their own citizens aging rapidly and not having enough population growth. I believe Germany is one such example."

That's interesting. Maybe this could help with demographic problems here in the U.S. For example amnesty could capture new tax and social security revenues from millions of younger workers. Demand might be lower at a legal minimum wage however.

I'm wondering why Germany doesn't implement and administer an immigration program like the Diversity Visa in use in the USA if they're so desperate to have migrants to shore up the shrinking population at home?

Only if you _never buy anything_. The supply of jobs is not fixed or finite. People, including you, both create AND consume valueble goods and services, wherever they are.

But if I work a 2400 Euro job for 1200 Euro, that is quite a difference. The employer pockets the difference, all I spend in my guest country is a bit on food and living.

The supply of jobs is finite imo - a warehouse needs 20 unskilled workers, they'll get 20 workers working for 1200 Euro instead of 20 working for twice the wage, so 20 local people in a town are left with nothing...

The question was: "does 1 job taken by an immigrant equal 1 job lost by a local?"

So the answer is a ratio, and it's probably not 1:1. Maybe it's 1:.5, but it's almost certainly not as bad as the 1:1.