If you've got:
- An aging population
- Big entitlement and social welfare programs that depend on a broad and self-sustaining tax base
- A lot of people who want to emigrate to your country to find paying work and make a better life for themselves
…then it seems to me like the sensible solution is to welcome those people and make it as easy as possible for them to become taxpayers.
When you start coming up with convoluted rationales for why that is not sensible, I tend to start wondering what it is that you are actually afraid of.