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.