I believe that there is, as you're still restricting life from a baby who clearly isn't wanting to lose that life by its instinct of remaining alive. One may then say, "Ah, but their life will still be burdensome anyway with their disorder, so we do the children a favor by ending it early" and I believe that a statement like this is still invalid. We are as uncertain of the future suffering of this person as we are their future joy. However, a baby with retardation or no legs or whatever-it-may-be can not live a fulfilling life in the first place if it is wholly locked out of that opportunity by being ripped apart in the womb of its mother, or having its child-wanting parents restricted from reproduction. The scriptures have said that we are to multiply ourselves by producing children. It does not say to "be fruitful and multiply, unless your child will be an imbecile, in which case, do not". Who are you to say that they are unworthy of life, over The Lord's will in having provided them with the potential for one? Are we to go by man's standards of perfection, in this endeavor to build a "proper society" in this wicked world, or God's, in preparing us for His proper society beyond this plane? To express this position, I must also consult a tale of Lord Jesus Himself, documented in the Gospel of John.
>As he passed by, he saw a man blind from birth. And his disciples asked him, “Rabbi, who sinned, this man or his parents, that he was born blind?” Jesus answered, “It was not that this man sinned, or his parents, but that the works of God might be displayed in him. We must work the works of him who sent me while it is day; night is coming, when no one can work. As long as I am in the world, I am the light of the world.” Having said these things, he spit on the ground and made mud with the saliva. Then he anointed the man's eyes with the mud and said to him, “Go, wash in the pool of Siloam” (which means Sent). So he went and washed and came back seeing. - Gospel of John, Chapter 9, Verses 1-7
Thus, the works of God may be displayed in all of the physically disadvantaged, then, and so to prevent a work of God from culminating is to smack His glory like a disobedient dog, and to do that is defiant to The Lord, and all that defies The Lord is evil, for evil is all that is contrary to The Lord's character, and so this idea is evil.