There are many movements in the world that support zero population growth. They always use famine and mass starvation as an excuse. But let’s look at the facts.
There are approximately 6 billion people on the earth today. You could take the entire world population and fit it into the state of Texas and everyone would have 1500 sq. feet of living space. That seems tight you say, but look at Tokyo.
There are 125 million people in Japan, 60 million in Tokyo all with about 1200 sq. ft. per person. They are not starving, in fact there are sushi bars and restaurants on every corner. Even New York City, with 12 million people has approximately 1600 sq. ft. per person. And people are certainly flourishing there.
So it is not as important how many people there are, as it is how they live, what type of system they live under. Are they free to determine their own destiny? Find their own job? Buy their own home? Shop where they want, or are they the pawns of a fallen structure? The numbers to keep an eye on is not those at the bottom, but those at the top. What kind of system is in place that is keeping people from surviving?