Most developed countries are quickly losing population. The ones that have a slight deviation from that trend is due to immigration.
Foreign labor is what will keep most of these countries afloat for the following 50 years.
Japan is a good example, they lose about 1 million every year.
When a person migrates, I would believe that the origin country has one less population. So why is it good that this person props up population in the destination country instead of in the origin country?
And why does the destination country need that persons labour and expertise, but not the origin country?
If the native population is becoming exterminated with or without migration, what exactly is the "country" that needs to be kept "afloat"? Your stock portfolio? Your treasury bills? Your real estate investment?
Most of developed economies dont need blue collar foreign labor in the future. Some dont even need it now. There are no industries in uk or france and this labor role is mostly to suppress wages (we ve seen it with brexit and english truck drivers) . For industrial nations like germany before they shot themselves you do need this labor until robots and automation makes them obsolete. Way before 50years and then being a nation with low immigration is becoming a key advantage for a country cohesion and future. Finally every country at 25% youth unemployment (like france and spain) shoould block all immigration beside highly skilled immigrants