If the fetus is a baby brother or sister, that could be upsetting to a sibling.
If the fetus is a lump of tissue, then there's no reason to be upset about it. It's no worse than a jar of kidney stones.
Right?
Right. That's the way it is. Always been.
Let me make an analogy. You have a pet dog and I kill him for fun. Will you be upset? Naturally. If I kill a strange dog that's attacking my pet, would you be upset about the strange dog?
Now, with a fetus, if it's not related to you, you may be less emotional about it because you know it's NOT related to you but if you know that the fetus is related to you by sibling, it's a different story.
You can observe the same in animal kingdom - relatives tend to bond together while they kill strangers, even within the same species.