I agree that is the fundemental difference.
However, the way I interpret your admitted discomfort with abortion even before the threshold of you believe is human life, is that you're not all sure the threshold you set is correct. If you truly believe (as some do) that before Point A a unborn child is not a human, then there should be no discomfort with abortion. As I said, that's why I can respect the logically consistent position that an unborn child is not anymore human than toenail clippings. It makes sense. I find it repugnant, but its internally consistent.
Saying, its not a human before this point, but I still feel a little uncomfortable killing it. I have to ask, why? It seems to me that you are not at all sure the threshold you've set is accurate. You even admit a child before that threshold is still somehow special - above objects and animals, even if you stop short of calling it human life. Pro-lifers on the other hand, don't have to worry about if our threshold protect all human life. The threshold of conception is a pretty safe bet. Maybe its too early. I agree that the debate of when human life begins is murky, mired in personal ethics, religious beliefs, and philosophies to go along with scientific knowledge and will probably never be resolved. That said, I feel very comfortable with the threshold I believe should be established. When it comes to protecting the most fundemental right of life, I rather err on the side of caution.