The answer is simple; it is because we are overpopulating and destroying our own planet and need more room!
Imagine if each couple were delegated 1 acre of land to live on, and could only use resources from that plot of land (catching rain water as needed). All their food had to come from that acre, all their waste had to be disposed of on that acre.
They build a house using all the trees and rocks. They plant a garden and have some chickens. They have a goat for milk. If they are lucky they have a pond for fish. They are perfectly sustainable on their land. Then one day they have a baby. That baby needs things. They re-purpose older clothes for baby clothes, but food eventually becomes an issue. At first they can produce enough to feed the child, but eventually the child needs more food and it gets tough with the parents eating a bit less just so the child can have more. Then they have another child.
At one point their small house starts to feel crowded, but they have no more trees to use to expand their home, and do not wish to take away any more land from what they need to produce food.
On land that previously supported two people, they are now trying to support four. What do they do?
|Vege patties, spinach, cucumber, tomatoes. A meal for two.|
They find ways to cheat on food production. They pump the goat with hormones so it produces more milk. They water the garden more so it produces larger vegetables and fruits, but even though the fruit is larger it contains only the same nutrition as would be in a smaller vegetable. Combined with the fact that the land has been used so much that it contains less nutrients than in earlier years, and we see how the family has barely enough food but the food itself has less value.
This is where the human population is now. Although we feel like we have unlimited space and we technically produce enough food for everyone, the food we are producing today has less nutritional value than it did even 20 years ago. Dairy animals in some nations are pumped with hormones to produce more milk but the side effect of the hormones on the humans that drink the milk are dangerous, and the dairy animals themselves have shorter lives as a result of being stressed in that way.
Our farmers are producing big strawberries, but have you tasted one or compared it to the small strawberries that grow wild? The huge berries have little taste in comparison.
Think of the earth as the one acre homestead. We cannot expand it. If we keep adding people to it, and resources are limited, we have to find ways to cope. We can cope by cheating with the resources, but to what end?
Additional problems come about in that some people are not happy with their meager one acre and insist on having more, thus forcing others to get by on less space, or poorer land.
If you had to live on one acre, and could only produce enough food for two people, would you have kids? How many?
I should note too that food is not the only issue we need to consider in regards to human overpopulation.
Sending people to live on Mars is not the answer. Killing people off is not the answer either!
The answer is for people to be more responsible. Having children at a later age (no younger than 25) and limiting oneself to only having one child is a good solution to prevent further population growth. It is also vital that people adapt sustainable skills, and stop demanding unnecessary things (useless home decor items, and other luxury items).