It starts to approach eugenics pretty quickly, which we as a society have pretty much rejected.
But we do regulate the raising of children, to a certain extent. For example, we regulate school curriculum to install a certain set of values and knowledge in children. As a society, we also attempt to regulate certain kinds of parenting, by making certain forms of child abuse and neglect illegal.
I was curious what you were trying to say. I assumed you meant that Down's Syndrome is down due to testing and abortion. But I found this:
The vast majority of screen-positive results are false, yet encourage invasive diagnostic procedures that pose additional risks to unborn babies. As a direct consequence many babies who do not have Down syndrome are lost. We estimate that current screening practice in England and Wales reduces annual live births of babies with Down syndrome by around 660 and leads to the losses of 400 babies without Down syndrome. Although prenatal diagnoses are becoming more frequent, more babies with Down syndrome are being born (up 25% over 15 years).
But we do regulate the raising of children, to a certain extent. For example, we regulate school curriculum to install a certain set of values and knowledge in children. As a society, we also attempt to regulate certain kinds of parenting, by making certain forms of child abuse and neglect illegal.