Abortion debate

There’s an absolutely fascinating abortion debate here. It’s between a pro-choice atheist and… a pro-forced-birth atheist!
Crazy.
It was pointed out to me by a friend, and I read it with great interest. I have a significant disagreement with the pro-choice guy, but I liked how he defined “person” and I like how he dismantled the pro-forced-birther’s arguments.

Firstly, the stuff I took issue with.
Mr. Carrier claims that

What is rarely understood in this issue is the fact that the most popular means of birth control actually partly relies upon inducing early abortion, and is very likely responsible for many times as many abortions as occur in counted procedures. Hormonal medications of this sort include “The Pill,” and Norplant, as well as the numerous herbal solutions which share the same or similar chemical properties and are thus employed in third world countries as a less expensive alternative to the manufactured pharmaceuticals that they mimic. All these chemicals operate simultaneously on many levels, primarily by preventing ovulation and hindering sperm, but also by preventing implantation (and thus causing expulsion) of an egg that, despite all else, is fertilized anyway. In other words, all chemical forms of birth control, including the pill, cause abortions–and no one can know whether or when they have worked by their primary means or in this last-resort manner.

However, this goes against what I have always understood as the definition of abortion, which is the act of ending a pregnancy before gestation is complete. Pregnancy, I have always been told, begins when the fertilized egg implants in the lining of the uterus or fallopian tube. My understanding is that over-the-counter pregnancy tests test for that event, not for the presence of a fertilized egg. I am also under the impression that the vast majority of fertilized eggs do not implant – if memory serves, my ObGyn has a poster saying that something like 80% fail to implant in a non-contraceptive treated womb.
The argument over when pregnancy begins, though, has the same problems as the argument over when life begins – it’s a matter of semantics and value judgements. Personally, I feel, as Mr. Carrier does, that prior to the development of a cerebral cortex, there’s no person, just a mass of potential. He defines a person as “an individual human personality,” and I agree – infants have personality traits, old people have personality traits, etc. A person who is braindead does not have personality traits and will only get them back if they get a brain transplant – but they will be different personality traits. Most people, I think, would say that if that happened, there would be a different “person” in the body than their was before.
No complex cerebral cortex = no human personality = not a person. For example, my cats have simple cerebral cortices and thus have personalities, but I don’t think they each count as “a person.” I care for them a great deal, of course, but I don’t think they have the same rights as I do. If I did, I wouldn’t keep ’em as pets.
I like Mr. Carrier’s definition because it puts into words what I’ve held as a not-well-formulated opinion for some time, and I give him kudos for it.