Why do most countries want to keep the populations fairly stable?

Answer 1

So that demands do not outstrip resources. When they do, then you have runaway inflation and poverty.

Answer 2

Western countries shouldn't. We have a demographic time-bomb around the corner. Our population is ageing very fast and we need to encourage gradual immigration of skilled workers over the next 20-30 years perhaps longer. It needs to be planned well so we have the infrastructure ready for the extra workforce and not to allow freeloaders.

Answer 3

To balance population with the resources available.The resources are diminishing and hence the even more pressing issue of population becomes.
This is a major issue according to Nobel Lauriete Wangari Maathai,and is indirectly the cause of war, diseases, poverty etc

Answer 4

Many countries are rethinking this issue and are concerned. To sustain population levels a fertility rate of 2.1 is required. Most all of Europe and Japan, and most Asian countries have fertility rates that have fallen well under 2 and are significantly below replacement levels. (The US is currently at 2.09.)
This is in the process of creating an enormous crisis in terms of funding a glowingly elder non productive population and retaining work forces that can sustain economic activity at acceptable levels. Production levels will become choke points for economic development and, eventually, lead to economic decline.
It also skews the impact of immigration. In Britain, for example, there is a political storm to keep out Bulgarian, Romanian , and other eastern European immigrants on the one hand, while on the other, the fertility rate is 1.7 and there are 350,000 Britons who emigrate out of Britain annually. You have a hollowing out of the society occurring here and in many other countries.
This is going to become a significant, vocal issue in the very near future as more and more people recognize its economic & social threat.

Answer 5

so that the populations will not outpace the resources of a country. Although, the amount of resources can grow, if the population grows faster, the country becomes poor and unstable.

Answer 6

sudden population growth or decline can destroy infrastructure