"So, then the question is whether it is appropriate to dispose of a fetus by abortion because it might be born with birth defects, or would it be better to allow the child to be born and to live with deformities which may or may not be serious."

Well let me answer it for you. Imagine you are confronted with a pregnant woman who has had Zika. Would you dare to put the question to her in the way you stated it here? How do you think she would see it, put the way in which you put it, coming from a Roman Catholic male? Or would you conceal that from her? Have another look at your wording. "Appropriate." "Dispose of." "Deformities which may or may not be serious." Wow.

What is appropriate is for her to have the facility to have an abortion freely available, without tendentious "advice" from people with different interests to her and without moralising from the religious. She needs factual and full information, honestly and neutrally presented, and she needs friends. Gosh, it sounds so hard. The reason it's so hard is because the default for most women in our so-civilised nations commonly approaches precisely the opposite of what I've just suggested. You're living in a country which is making it harder and harder all the time for women to make the free and informed choice whether to have an abortion or not. Your question is part of the problem.