The foetus is not part of the mother? Then you go along with the 'parasitic infection' school of argument, used famously - and I presume with some degree of irony - by radical feminists to argue in favour of abortion?
The parasite analogy is purely emotive. It is just an elaborate way of saying: ‘You wouldn’t like it if you were in that position!’
If there were a race of blameless parasites with such a high probability of achieving free-living sentience, contracted so frequently in such a well-known and easily avoidable way, my position would be exactly the same. It would be a great evil to kill them. I do not have any irrational reverence for human life in particular: our slimy tentacular co-sentients are equally deserving of our consideration.