The argument is made that a fetus is not a human being.
I don't know at which stage of life that a fetus becomes a human being if at all.
and the argument was once made (and legally supported) that black people are 3/5ths of a human being.
Our laws evolve.
I believe that a fetus is a human being and deserves protection under our legal system. Scientific evidence supports that conclusion as does common sense. If a fetus is NOT a human, then what is it? An banana?
At any rate our legal system has two major pillars that support protecting a fetus:
1) To err on the side of life. If we are uncertain in a death penalty case - we have decided to err on the side of life - not execution. So if we can't be certain about when human life actually begins (and not just trying to massage a guilty conscience, but REAL questions) then we should err on the side of life and protect the fetus.
2) One HUGE reason for laws is so society can help protect the rights of the weaker - those who are unable to protect themselves - from the stronger who would trample their rights for their own convenience. That principle demands that we protect fetuses.