Right now we have about 7 billion people on Earth, right? Suppose the entire world was Catholic, and followed NFP teachings and had a family of between 6 and 12 children. The median family size would be 9 children, or 4.5 per person currently living. In one generation, our planet’s population would go from 7 billion people to (7 x 4.5) 31.5 billion. Could we really support 31.5 billion people?
If this hypothetical rate of reproduction continued for two more generations, we would have 637 billion.