A neutral birth-rate is just perfect
but it's not neutral, that's the point.
1.4 children being born for every 2 parents = a declining population. those parents then retire and each year, less and less people are around to support your retiring population.
"After a long decline, birthrates in European countries have reached a historic low, as potential parents increasingly opt for few or no children. European women, better educated and integrated into the labor market than ever before, say there is no time for motherhood and that children are too expensive anyway. The result is a continent of lopsided societies where the number of elderly increasingly exceeds the number of young - a demographic pattern that is straining pension plans and depleting the work force in many countries.
The European Union's executive arm, alarmed by the trend, estimates that, if birthrates remain this low, the bloc will have a shortfall of 20 million workers by 2030."