You consider that re: slavery laws, the person with the most to gain or lose is the slave owner, vs. the slave.
Yet when you consider abortion, you assign the baby as the person with the most to lose.
I know this is a side issue (to a side issue), but why don't you think that the person with the most to gain/lose under slavery laws is ... the slave?
It's a little more nuanced than that. There are two questions.
First, the humanity of the baby/slave is in question. The mother/plantation owner gets to decide what the answer is. They have the most to gain or lose from the question, and therefore have a conflict of interest in deciding the question.
Second, obviously, if the baby/slave is human, then they stand to gain/lose the most from the next question - should they live or die - because there's a human life in the balance now.
Obviously the slave is going to insist that they're human, and it shouldn't be up to the slave owner to decide that they're not, just because it's convenient for him.
And presumably the baby would as well, except that it has even less power in this situation. It is generally considered a virtue of our society, that we try to ensure that even the powerless and voiceless have an advocate for their wellbeing.
Giving one person the privilege to decide that someone is not human, simply to realize some convenience for themselves, seems like a bad idea.
To be clear: If the baby isn't human, then it has nothing of significance to gain or lose from the question of whether it should die. The problem is deciding who gets to answer that first question.
In the case of the slave, we might say that the slave gets to answer that question. But actually we've already agreed that the slave is human. We've already agreed that the slave owner cannot unilaterally declare otherwise. We've already agreed that he does not in fact own the slave.
We've agreed to none of the relevant stipulations about the baby. Francesca and others want to avoid the question of human life and death entirely, by simply letting the mother decide if its human or not. I think that is a mistake. No one person should get to decide if another person is human. Especially if denying the other's personhood stands to benefit them in some way. We don't do that with slaves. We don't do that with soldiers. We don't do that with prisoners. I don't see why we should do it with babies.