This morning, I was thinking about it from the other end: let's say contraception is immoral -- the termination of a potential human life -- regardless of circumstances. G-d wants us "to be fruitful and multiply" and this axiom applies without limitation. It follows that contraception isn't just wrong for me, but wrong for anyone, anywhere. Immorality is bad; the world would be better off if no one committed any immoral acts.
Following this, I'm trying to imagine what the world would be like if no one used birth control. Since I'm imagining a perfectly moral world (by Christian standards), I can further posit that sex only occurs between married couples
Estimated current world population is 6.2 billion. About half of those are women: 3.1 billion. It's hard to estimate how many of those women are of child-bearing age; about 1/3 of the female population in the US is between the age of 15 and 39. In Algeria, that figure is closer to half. I'll be conservative and say 1/3, and round down: 1 billion fertile women. (The preceding statitistics were gleaned from various parts of the US Census Bureau's web page. The following guesses I extrapolated in their entirety). Let's say that, of those women, 30% are unmarried, for whatever reason (too young, choosing a life of abstinence, etc. This is a purely out-of-the-air estimate, take with a big ol' lump of salt). That leaves me with 700 million childbearing-women. I'll assume that, absent the use of any form of birth control, these women have one child every two years. (This factors in the effect of breastfeeding, which makes women less likely to conceive while they are nursing. Or maybe it make th zygote less likely to attach to the uterine wall. I don't remember the specifics of the biology involved).
That's 350 million babies a year. Now I need some mortality statistics -- the mortality rate in the US is 9 per 1000, let's just double it for the world, that'd be 18 per thousand. At the end of a year, we'd have 6.55 billion people, of whom about 118 million would die. Net growth puts us at 6.432 after one year. Wold population growth rate would then be about 3.75% per year. (The real-world estimated growth rate is 1.25%.)
That would give us the world's population doubling approximately (very approximately) every twenty years. (Wow, I can remember when a teacher told me it already was! According to a 1998 Census Bureau report, the actual world population in 2050 is estimated at 9.3 billion, suggesting a doubling rate of closer to once per century. For the 20th century, world population doubled about once every 50 years.)
So, in 2022 we'd have 12.4 billion people. In 2042, 24.8. In 2062, 49.6. In 2082, 99.2. In 2102, almost 200 billion.
I wonder if science could keep up? Improvements in agricultural techniques have allowed us to continue to (mostly) feed our current ever-growing population. But to feed 32 times as many people as we have now, we'd need to improve a lot faster than we have so far. If we put all our resources to it, could we? The earth has 197 million square miles of land. We'd have about 1000 people per every square mile of the earth...and mind you, a lot of that is in places like Siberia. Suburbia would have to go. We'd need to colonize the seas, if not other planets. Unless FTL were invented, colonizing another solar system would be even more challenging, since any colony ship would need to accomodate the ship's population growth rate over the course of the journey.
I wonder if we could make it work?
If Earth remained the only habitat for humanity...I can't imagine that I would like it by then. By 2200, there'd be over 6 trillion people. Trillion! Wow!
One thing's for sure -- you'd definitely have to posit scientific advances as not merely a good, but an absolute necessity. Either that, or go the othe way and say that famine, disease, and death are all positive goods ... because without huge technological changes, they'd be inevitable with that kind of population growth.