you have hit on the exact point, which is where genetic research and such is leading. Long before we have a cure for birth defects, we will have the "solution." Identify them in the womb and eradicate the "imperfect."
Of course, as that progresses, the definition of "imperfect" becomes more broad, and the pressure to "design" your offspring comes in.
Why would you burden society and yourself by bringing a child with a disability in to the world?
SD