I think you're confusing overcrowding with overpopulation. I think they're two different concepts and that's where we're talking at cross purposes.
The surface area of the earth including water is 500 million km or about 200 million sq miles. or in feet at about 5000 ft per mile-- 5000 X 200 = 1,000,000 million square feet... so if a guy uses up 4 square feet, that's 250,000 million people packed into 4 ft square areas... that's 250,000,000,000.... which is what... 250 billion.
In my highest estimates of population for the Earth, I was thinking 100 million... less than half of that... which gives everyone an 8 ft. cubicle... not counting up and down space in mutistory buildings. But the world is 3/4 water so only 1/4 of the 8 ft cubicle is land... leaving 2 square feet at 100 billion.
We're at 6 billion right now... which is less than 1/10 of the 100 billion... so that leaves us about 20 square feet per person right now.... does it seem to you that it's overcrowded now at 20 sq ft per person? Numbers don't lie but it seems to me that a calculation like this has limited value.
I would think that with higher power density and new materials.. and a good technological rate of progress, we would be populating off-planet at roughly the time we hit a healthy educated 20 billion here on Earth... so that by the time the total human population in the universe hits 100 billion, at least half of that will be off planet at any one time.
Maybe population studies will become more interesting than I thought. Thanks for making me think this through... if my numbers are wrong, please point it out. I'm willing to look at it. I just think that arguments against population increase are phony arguments directed at overcrowding and starvation etc... although i can't get a handle on it yet. There's no magic number for earth but as you can see-- if we see ourselves living in a pop density for earth right now at 20 sq ft per person, it's not as bad as the number tells us it is. Therefore at 2 sq ft per person, that number would not literally be that either.