No, actually, the Supreme Court helps us decide.
Even the Catholic Church abandons your "personhood" argument for the unborn when it suits them. Just look at the suit against St. Thomas More hospital right now. They're main defense is that a fetus is not a "person."
Don't try to lecture us on the left about what we get to "determine." Particularly when you are simply trying to determine the same thing, with just the opposite conclusion. The right expects us to accept their morality, and then condemns the world for imposing their morality on the world when it deviates from their own. Hilarious.