population stability?

I was wondering if Eduardo would expand on why "population stability" is the question on which we ought to focus. Even the United Nations is now admitting that the problem in the West is that birth rates are too low. As Catholics, we ought to focus on the blessings that God showers on us through our children. This is not to say that couples are required to have as many children as possible but I don't think that "population stability" ought to play much of a role in a couples exercise of responsible parenthood.   

Richard