Human beings are the most valuable factor of production. Those who do not contribute to reproducing this key factor of production should have drastically fewer pension entitlements than those who both save and propagate.
Most of the developed world is now in need of pronatalist policies.
It is crude materialism to consider procreation in purely economic terms and as a key to sustaining the future output of the economy.
Encouraging parenthood is a reactionary product of certain religious beliefs (notably Catholicism) or nationalism.