Some abortion advocacy groups call the "right" to abortion a human right. But the term "human right" suggests that it's a right one has by virtue of being human, and that means humans possess that right as long as they exist, at all stages of their lives.
So the right to abortion is something human beings have from the very beginning of their existence, which is at conception. Thus the abortion advocate faces this paradox: the unborn human being, by virtue of being human, has a right to have an abortion, but has no right not to be intentionally killed in the womb. (Amherst professor Hadley Arkes develops this point in "Natural Rights and the Right to Choose.")
There's a similar problem when abortion defenders invoke "human dignity" and "equality." If human dignity is possessed by all humans, then it is possessed by the unborn human beings who are killed by abortion. If human equality is real, then excluding one class of innocent human beings (the unborn) from legal protection is unjust.
It's revealing, I think, that abortion rights advocates tend to borrow pro-life principles when defending their own view.
