I have to trust in nature taking control (much like brettd states). As resources are deplenished, or eliminated, people will simply be forced to look for other means. Those who have the capability to control those means will be the ones to flourish. Unfortunately, I do not think examination of birth control will help the problem. As justaguide points out, just because people have less children does not mean they will work harder to bring more money into a family.
I simply do not think that there is a way to force birth control. For example, look at the criticism that some countries have taken given their harsh birthing laws. For some, education simply does not work.