A fully-formed human has more rights than a partially-formed human.
It’s that simple. To add:
I do think that once the fetus is viable that it is immoral to abort: at this point the fetus is nearly fully formed-certainly more fully formed than partially formed, given that it can survive outside of the mother’s womb. Once the fetus needs no longer to rely on the mother, it is very obviously its own person, since it does not rely on another’s body to live. Prior to this however, it is not reasonable for the fetus’ rights to outweigh the mother’s.
