Forgive me for citing from a science fiction show, but I think Geordi LaForge from Star Trek: The Next Generation handled this issue best. In one episode they visited a planet populated by colonists who had sealed themselvves off from the world in an attempt to construct a perfect society. This included physical perfection; one of the colonists sheepishly admitted to Geordi that his congenital blindness would have been detected in utero and he would have been aborted. Geordi asked, "And who would they be to decide that my life was too difficult to be lived? Who are they to decide if a person like me gets to exist?"
Major birth defects are tragic, but abortion compounds the tragedy and is the worst sort of playing God.