The Darwinian worldview leads to euthanasia, abortion, sterilization, and genocide. If we assume the truth of Darwinian evolution, that is the simple and logical conclusion; as Hitler's propoganda stated, no good animal breeder allows the unhealthy or inferior animals in his care to breed. If we, too, are just animals, somewhere between apes and supermen, then why would we not want to assist the progress of the species by cutting out those who obviously will not be helping us toward the latter?
The Christian worldview stands in stark opposition. The Author of life claims responsibility for making the deaf and the blind. (Ex. 4:11)
In the Christian worldview, there is no such thing as a "defective" person. The child with Down Syndrome, the cross-eyed man, the woman lame from birth, the deformed, the mute, these people were not rejects from the celestial assembly line.
Certainly, there are natural factors that God uses to bring such things about- some of which we are responsible for.
But the basic Christian assumption is that God made you how He wants you.
We are responsible for what we do with what He gives us; we are responsible to invest our talents wisely. But He is the One Who gives the talents as He sees fit. (Matt. 25:14-30)
Sterilizing the "inferior", as America did in the early 1900s, or committing mass acts of genocide, as the Nazi regime did, or murdering the unwanted in the womb like we are doing by the thousands and ten thousands today in this country- this all makes sense if we are the judge of what is "viable," what is "superior," if we can control the factors and predict the results- and if we are not accountable to God for what we do with His souls.
But if God makes people individually by His hand, then it doesn't matter what the child's pedigree is. If God wants him blind, He'll make him blind. If He doesn't want him blind, then the child will not be blind. If the child is blind, there is no blame or shame. That was God's perfect will. That is just as much a person, a life, a soul, in the words of Lewis a "self." And if that child is chosen by God, then he is just as much a member of the Church-Bride of Jesus Christ. God wove that human tapestry and signed it with His image and bought it with His blood. There is no higher pedigree than that which is held by the child of God.
Blind or not, "normal" or not, we do not have the right to determine that life inferior. We can only judge things which are under us. Human creations, human actions. Life is a creation of God. He has the right to tell us when- and why- we may take it from another.
We did not give it. It is not ours to take unless the One Who gave it tells us to.