The set of incongruities needs to be resolved.
Genetic fatherhood begins at conception.
It makes zero sense to say that the man’s genetic fatherhood is irrelevant when he wants to protect his baby from being murdered between conception and birth and yet relevant when it comes to extracting 18 years of cash from him.
The obvious resolution is laws that ensure that the man can legally protect his baby between conception and birth.
Laws in some states, Texas among them, had child support being only extracted for children born in wedlock. This acted as an incentive for women to marry.
In 1973, the Supreme Court overturned that, with predictable consequences.
https://caselaw.findlaw.com/us-supreme-court/409/535.html
GOMEZ v. PEREZ(1973)