Personhood Question is Key
When Supreme Court Justice Harry Blackmun penned the 1973 Roe v. Wade decision which legalized abortion in the United States, he admitted:1
If this suggestion of [fetal] personhood is established, the appellant’s case, of course, collapses, for the fetus’ right to life would then be guaranteed specifically by the [14th] amendment.
The appellant was Roe, and the 14th Amendment states that “no person shall be deprived of life…without due process of law.”
In other words, Roe v. Wade itself acknowledges Premise 1.
Pro-lifers tend to take this for granted, but not everyone does so. Many pro-choicers contend that abortion should be legal regardless of the personhood of the unborn.