That's assuming it's a closed population. The PGR is calculated with the birth/mortality rate and the immigration/emigration rate. Believe it or not, in some developed countries, the birth/death ratio is 0 or less. If there wasn't any immigration, they'd die off, slowly. And also, China has birth limits. This is due to their mass population. So the birth limit is a fair idea, depending on the situation. Now, since I'm assuming your American or European (Sorry, I'm new o.o;), I'm also assuming that's why you would be against a birth limit. Heck, in my country, I would too! Now, if I were to run my own country, I'd be a terrible dictator. I'd ruin my country and end up being rebelled against where I will eventually get mutilated. But I'd have my great fun before the end. I'd go into greater detail but I'd be called insane ._.