This debate will spark a lot of hate about freedom, however the answer is very simple. A birth limitation is necessary in the United States. As more and more people are unwilling to work and very willing to freeload, the production of unwanted children should stop. People should be able to have as many kids as they can support. Once they have a child that they cannot support they should be unable to have another. If you can pay for the first two but falter on the third, you should be unable to have a fourth. This is just simple economics.
Even though the world is overpopulated, birth limits lead to a plethora of civil rights violations. Lawmakers will believe that since they can limit citizens on the number of births, they can place many other limitations on citizens' private lives as well. Family planning is also a very personal decision that each couple needs to make, not lawmakers.