Actually, it’s simpler than that.
Pro-lifers believe that human life begins at conception.
Pro-choicers believe that human life begins the moment the child is passed out of the mother.
And that’s the critical difference.
The willfully-held fantasy that the child changes in nature by passing through the birth canal is the fig leaf employed by some “pro-choicers.”
But there are millions of “pro-choice” people who simply do not care about the nature of the child at all. They want the liberty to kill it; the government says they can have that liberty, if they just vote for the right people; and that’s all they are concerned with.