I was recently involved in a discussion about a sperm donor (or his estate, if I recall correctly, but it isn't important) being sued by a lesbian couple to whom he had donated his sperm. A child was born, the child was adopted by the lesbian couple, the male donor's estate was sued for money.
The knee-jerk reaction to this kind of case seems to be that it is wrong to view the natural parent as having any obligation to support the child once the child has been adopted by another. But that knee-jerk reaction is, in my view, wrong.
Parents have an unbreakable and permanent natural law obligation to provide for their children. Adoption is one way to provide when the natural parent is unable to do so directly: it is a mercy available for the sake of an otherwise impoverished child. In adopting a child, another person or persons take on a parallel parental responsibility.
But adoption cannot break or in any way impair a natural parent's obligation. If a man gives up his child for adoption because he wants to party and doesn't want the responsibility, he has done a wicked thing. If the adoptive parents fall on hard times and can no longer provide, or if the natural parent comes into means, then the natural parent has a moral obligation to provide.
This doesn't mean that the natural parent would be in the right to attempt to take the child back: that would only be the case if it was in fact best for the child to be taken back as opposed to simply getting outside support in her present circumstances. If the adoptive family is a healthy place for the child to be, then the natural parent may have an obligation to keep his nose out of it and write checks. Deal with it, Dad: you fathered the child.
I think this unbreakable natural law obligation is one of those things that we can't not know, at least at some level. This in turn drives people to choose abortions: they know that once they've brought a child into the world, that child forever has legitimate claim to their support; and that nothing can break this obligation.
And what more efficient way to deal with an unwanted creditor than to kill her?