For every child born who manifests retardation or other disability there are probably dozens more whom Nature curtails anyway ... ones whom we don't get to learn of.<quoted text>
Doesn't work. AGPAR tests, checking breathing and color is all they can do at birth. Most retardation or developmental delays aren't picked up by a paediatricain till 18months to 2 yrs. By then your infanticide option is dead in the water.
Besides,'rushing to judgment' does not necessarily enrich Humanity.
A European family had a history of congenital deafness. The parents were deaf, and of their 5 offspring 4 were deaf and the fifth was expected to become deaf, in a day & age when medical and other support was not what it is today. If Euthanasia had been trendy back then, the World might well have been deprived of Ludwig van Beethoven.
A baby was born so premature that he was not expected to survive. His neck soon proved to be so weak that he was never expected to be able to hold his head up. Rather than let Nature take its perhaps cruel course, his parents persevered valiantly, commissioning a neck brace to be made support his head, necessary until well into his childhood. And a good thing that they did, else the World would have been deprived of Isaac Newton.