The value of a human life is how well off/developed society is.
Take for example the construction industry in the U.K. its about 72 this is hugley reduced on from just 50 years ago. Is one life worth a 10,000 buildings? a 100,000 buildings?
We as a society accept this but would we accept the number of deaths from 100 years ago which could be as great as 1 per 1000 buildings? No we would not hence all the health and saftey we have today which saves many lives, but this is a product of a more advanced/wealtier society.
Yes the loss of a human life throughout history is always regarded as a loss but the value of that life has changed. A deformed baby was seen as an acceptable accident of pregnancy much like a miscarrige. Unfortunate yes but just one of those things that life throws at you.
The practice of only killing killing deformed babies is quite moderate compared to many areas of the modern world, some areas of asia there is 3 men to 2 women as girls are seen as less valuble (dowery/unable to support the parents) and killed at birth. Or take China which can kill a nearly born healthy baby if the parents voilate the 1/2 child policy.