I am still on the "where is it in relation to my body" as a point of reference.
If I start a blood transfusion, and they stick needles in my body and start sucking it out, I still have legal right to change my mind and stop giving blood to that other person.
If I start organ donation and they do surgery prep and I'm on the table with my buttocks exposed, I still have legal right to change my mind. It'd be complicated and sorrowful and devastating to others, but I retain that fundamental right to control of my body. I can actively take control and perform actions within my body that may have negative consequences to others, that may not be nice or beneficial to others, but still remain firmly within my control.
It may come to another perspective as well: am I actively murdering the person within me, or am I withdrawing services I am providing to another person within me.
Circumcision: The skin of the penis in male babies can be taken from us with out our consent.
Conscription: Think about drafted war veterans who have lost limbs and such. They should have had the autonomy to keep those body parts, however they were forced to sacrifice them for the sake of the state (think about how we say soldiers give their lives, for their country.)
Also, the organ donation is a variation of Judith Thompsons violinist, which has been criticized already https://rintintin.colorado.edu/~vancecd/phil215/Warren.pdf
If someone stole blood from you, and if you take it back the person will die, are you permitted to take it back? I don't think you are. Of course most people permit abortion after rape, so you need some other kind of justification for that, but on an intellectual level, this one will not work. You need a different argument.
> We can take opposing positions on that, but I think understanding that both positions exist is required for honest discussion.
That is definitely a very interesting question. I feel you would have to distinguish between a pill taken before implantation (birth control) and a pill taken afterward (plan B).
One prevents it from ever happening, the other destroys something that did happen. To me they are different.
Also, I must point out that none of this discussion informs my position on early abortion (although it does inform my opinion on abortion later on). So this discussion is more intellectual than practical. I say this to argue with your position that this line of reasoning transformed your opinion - I strongly disagree that this is a good line of argument.