I flew to Cancun Mexico from Cali a while back, I had a window seat and was surprised to see that every time I looked down all I saw was green. This went on for about 6 hours. No people, no houses, no lights, no nada except for green. An acquaintance of mine told me about a 36 hour train ride is Russia where all he saw was pine trees and snow. Look at earth from space, most land is uninhabited and green. What's killing the earth is irresponsible industrialization. There's plenty of room for everyone if we learn to live responsibly. The third world should sterilize us and continue to have kids and enjoy life. My Mom always warned me that the world wasn't fair though so....
The fact that you can see a lot of undeveloped land in various parts of the world does not mean the world is not over populated. If you did away with skyscrapers that allow people to live one on top of another and gave everyone a single family home on approximately 1/3rd acre of land (average single family home yard size) you would see much if not all of that undeveloped land disappear. The issue isn't that the world can't support the population we have now but rather can't support the population that is coming very soon. It took us from the beginning of Man until 1960 to reach 3 Billion. It only took from 1960 to 1999 to double that. The population is growing exponentially and the world's renewable resources can't keep up.