Just because you can physically fit 9 billion people in the State of Texas doesn't mean that they would live for long in such conditions.
So do you think illegal immigration is an economic boon to the USA because of the extra population it provides?
If not, why not?
9 billion people may well live comfortably and happily upon the Earth, with better utilization of resources - that may or may not be the point of “overpopulation” that leads to demographic contraction due to epidemic or starvation or warfare or whatever the ‘release valve’ of the overpopulation ends up being.
The Earth, with better technology, may well support 14 billion people in health and comfort.
And it looks like we had better start planing for such, because despite the idiotic ramblings of a not very bright religious devotee, the Earth's population is increasing and AT an increasing rate.
Actually you can physically fit 9 Billion people in the State of Rhode Island and still have a bit of room leftover. (BTW the answer to the question is 0 States.)
Further I never advocated allowing any illegal in here I am for a Wall on all borders manned 24/7 by tough Hombres like the Marines with orders to shoot to kill anyone trying to get in illegally!
I just point out that the Point is that the Overpopulation Myth is just that MYTH! If we take ALL the people of the world and set them up in the USA spreading them out so they could live comfortably then you would have the rest of the Earth to farm and use for Resources. Point is the EARTH is HUGE in comparison to the Human Population. And the only reason their are people going hungry right now is that Governments are so inefficient at handling resources that they waste more than they use to produce anything.
It is the very reason why Socialism doesn't work. You want everyone fed and happy them give them property rights and toss these Socialist Governments (Starting with the Obamanation) aside and you will see Prosperity Worldwide.