Yes, we will learn so much.
No, it's unethical.
It's a volunteer. While I am not pleased with potentially killing the baby, even for science, it's preferable to abortion which is just irresponsibility. But if the baby is conceived in outer space, then the baby would have no chance at life if I did not pick "Yes". I do worry that the baby would be extremely weak on earth though, since the heart would only have to pump very softly to get blood around. There are reasons we picked incredibly physically strong people for the first space flights. But again, better the baby have a small chance of living than no chance at all.
If they volunteer, then why not?
If we want to eventually become the space fairing human empire that I hope we will become, we have to know these things.
Only if we try another mammal being born in space. If that goes fine without a miscarriage, we could try a human born in space.