Paying full taxes to support a society where people with kids pay less taxes and receive more benefits from the State is certainly not selfish. That's the case in my country, at least.

Money is not the only way one can contribute to one's society. Doubling the amount of productive people to society is also a big contribution.

Even from a purely financial perspective you need to count all of the future taxes that will be collected from the family lineage instead of just from the one person who ended his lineage.