Elrond by yoru own reasoning a baby should only have rights when it can consciously decide. Thats the impression I got from your analogy. But in that case the child would be about 9 - 10 before it can decide, and thats highly unreasonable wouldn't you say?
I propose that as long as a baby is inside a person that baby has no rights. It is only until that baby is seperate from the mother can it have right.