Birth control should be encouraged in all countries where a majority of the people live below the poverty line. This questions is ambiguous because there are large parts of the world such as rainforests which have low population densities compared with overpopulated areas like Calcutta etc. It seems over-populated because men choose the area they want to be in. And if you look further, theres more space than enough. Birth and death are in the hands of allah with all the predictions of great number of people to be dead at a certain year because of aids cancer and other diseases not even mentioning of the millions that die of natural disasters.
World is over populated yes but islamic knowledge is less.
It would not be overpopulated if we could learn how to sustain ourselves and grow our accomodation of people as fast as the population itself. Allah knows best. It is not at all populated. The population need to be increased. It is all Shaitan plot to develop such thinking that world is populated.