Running out of space: If every human stood shoulder to shoulder it would only take up the state of Road Island. If we would spread out with the density of an average city, we would fill the state of Texas. Overpopulation would take billions of years to fill the entire world, and by that time things are likely to be different. (3)
How many countries have the problem: Right now only China, India, and Indonesia have this problem. So many more countries are in a desperate need of babies like Germany and Taiwan. Countries like Russia and France are in such a need that they actually pay their citizens to have babies.(2)Don't forget that a lot of these countries are not in need of more or less population, they need a stable growth.
Economy and Resources:
The size of populations don't have an effect on the use of our natural resources. 5 billion vs 10 billion; WE STILL ABUSE "This is the result of despotism, corruption, economic ignorance, short-sighted greed and the inhumanity of man unto man - it is not a matter of counting heads." (3)
As far as the economy goes, income rates stay steady if the population increases or decreases at a steady rate.
The problems that some counties do face is when there is an immediate spike up in population. The US saw this in the baby boom of 1946 after WW2.
I can go indepth with the supply and demand of people but, I'm not because it would take up too much space in this post. I am eager to read my opponent's arguments and debate more.