Ultimately the popularity of this objection today is a reflection of a shift in world view.
People used to view their bodies — in fact all human bodies — as temples of the Holy Spirit (in a Christian context). If some ruffian broke into your temple rudely and put a treasure in there, you wouldn’t chuck the treasure out just because of what the ruffian did. Now you might hold the ruffian responsible for fixing the damage as best as possible, but you wouldn’t chuck out the treasure.
One’s view on the sanctity of life depends *almost* entirely on one’s belief in God. You will never convince an unsaved person that the seed of a rapist is a “treasure” in her womb. Sorry.