More people in the world means there is more land needed to be used to shelter them and more farms needed to sustain them food wise. This will kill animals and destroy ecosystems. Many endangered species such as tigers and elephants would be killed by humans coming in and taking their habitats for their own use whether it is for farming, producing, or housing. This can be prevented by reducing or stopping the increase in human population.
The increase in factories is imminent to keep producing at a rate to satisfy the increasing population and the increasing needs of the aforementioned population. This increase in factories will lead to an increase in pollutant emissions into the atmosphere that will increase greenhouse gases that will heat the earth and create even more problems. Also an increase in housing will add to the increase in pollution which will also increase destruction to the ecosystem by killing plants and animals with smog.