Easy for you to say.
What is easy for me to say?
Birth defects are not by design, they are defects in the building process. Anything a human can design can be built improperly. A complex computer can have a hardware "glitch" in the manufacturing. A single car out of many can have been built wrong though the design is sound.
I have never heard a genetic specialist say that birth defects were from "bad design". It almost always happened because of some external environmental issue or because there were certain recessive genetic traits that ended up showing up.
Given how complex human life forms are it is amazing it doesn't happen more often...