Switzerland is way crazy strict on immigration and there are heavy restrictions on EU citizens that try to work there. How many refugees do you think Switzerland took in?
I also don't know when banking became niche, but it's cute that you think that Switzerland was prosperous because of the EU when they are pretty much the only part of Europe that tells the rest of the continent to go fuck itself on a regular basis. Horrible example.
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I never asked what the sustainable population limit was for the USA, but rather at what point additional immigration would become a net loss for the country. In your scenario, you'd be cool with immigrating ~650 million people into the USA without any regard for the social consequences. Do you really think the country would be better off if we did that overnight? I don't think we'd have the infrastructure to handle it let alone the impact of government services.
Keep in mind, I'm not talking about immigration from just south/central America. I'm asking about immigration from anywhere because eventually you can't take in more migrants because as I pointed out before, immigrants (all races) are more likely to end up on government assistance than people who are native born. You'll run out of money at some point. Wouldn't it be cheaper to just stop subsidizing abortions at planned parent in the hood? Doesn't that hurt economic growth?
There are obviously other variables to consider but I don't see anything but arbitrary numbers and "this sounds good so i'll say it" talking points. I don' think GDP growth is the only measurement we should take into consideration but it's certainly a big one.