You know what? You're completely bonkers to think that god would allow Satan to **** up his work.
Unfortunately, Jesus Himself talks in the Gospels about Satan taking away from you God's presents that God gives you so that you can afford your life. If you don't have the Holy Spirit inside you, then you don't have the power to keep God's presents aka works inside you. Bummer? This is why human sinning is a problem. So God doesn't allow Satan to **** up his work, you do. And you can undo that with repentance and prayer.
So I can undo retarded and deformed babies with prayer?
I can smell that you didn't think through your word 'undo'. So I will answer, that between your two choices which are technology or prayer, your leftist pride will force you to pick the wrong one. Hehehe.
So you don't know why god lets deformed or retarded babies happen. Got it.
I have given you a part of the picture, you can figure the rest of the answer, but in case you get stuck, consider for example the blind man from birth that Jesus healed. When they asked Jesus whether it was his sin or his family's sin that he was born blind, Jesus told them that neither, but instead so that the work of God can be displayed in him. So there is the answer to your question of why, as well as the attached forgiveness and prayer to miracle stages.