I got to thinking that the immigration issue is like USA, Canada, Europe and so forth are life boats in an ocean. Some people are drowning, in that ocean, due to totalitarian governments, gangs, poverty, climate change and so forth.
How many people can we rescue before our lifeboat sinks? A question with no definite answer.
If we had twice as many people, in USA, as we do now, we would still only have half as many people as live in India today. We now have around 335 million. Twice that would be 700 million and double that again would get to the 1 billion 400 million population of India; now the world's most populated country.
India has surpassed China in population and has less land area than USA or China. Most people seem like they are at least surviving and maybe even thriving in India. I don't hear as much trouble, from India, as I do from some other countries.
Still we likely couldn't accommodate that many people given the circumstances of USA; lifestyles, expectations of wealth, infrastructure, housing, traffic, water use and so forth.