Overpopulation and Immigration

One reason people often give as to why we should be restrictive on the amount of immigration we allow to the U.S. is the concern of overpopulation.

What precisely is meant by "overpopulation"? Presumably, this refers to the point where population becomes so dense that it causes average living standards to decrease. How would we determine the population density at which this would occur? I doubt there's a good way to know for sure. But population and living standards, both within our country and globally, have been rising for quite some time. And since our living standards are not increasing by some act of nature, this means that for a good amount of time now, the average extra person added to both the world and our country has had an overall positive impact on society. Unless we just hit the peak, we clearly aren't overpopulated now.

And it must not be global overpopulation that comes to mind when people voice this concern. Because a person moving here does not increase global population. In fact, being in a society of greater wealth and freedom leads to people having less children on average. So if global overpopulation is a concern, allowing more immigration from poor/oppressed countries to rich/freer countries might be a good way to deter that. It seems the "overpopulation" concern over immigration is about the overpopulation just of our country.

So how populated can a nation get without it causing a necessary drop in living standards? What if we doubled our population? Tripled? What if it increased a hundred times? Our initial intuition probably tells us that surely we'd be overpopulated well before we multiplied our population by a hundred. But why would our intuition be good at determining that?

Population densities per country can be found here. The U.S. has 84 people per square mile. That's really low by global standards. Singapore, on the other hand, has 19,863 people per square mile. That is 236 times our population density. And their average living standards are even higher than ours (by a good amount actually).

On the list of things to worry about for the U.S., put overpopulation at the bottom.