At the end of World War II, world population was growing at the rate of 2% per year. This rate of growth has gradually declined, to where it is approximately 1% per year.
There is a lot of moaning and groaning over this decline, but, truly, here the devil is in the details, and in the numbers.
If the population continues to grow at the rate of 2% per year for the rest of this century, there will be 40 billion people on earth by 2100. If the reproductive rates stayed the same 2% for the next century, by 2200 there would be 320 billion people.
Obviously, this would become a huge problem; every ones quality of life would go straight to hell, with unimaginable consequences, none of them good.
Something to think about when people urge abstinence, and decry birth control: it could be the best idea since Einstein.