So...given this situation, the ***ONLY*** possible answer to questions like abortion and harvesting stem cells is...If you don't like it, don't participate! And do not presume to tell others how they should behave in their own personal lives.
Just to make my position clear, I describe myself as a scientific rationalist, as far as religion is concerned, I quite like Ignosticism.
Having said that, I'm sorry Bill but that won't do. If you saw Group A cheerfully slaughtering Group B on the grounds that they were in some way sub-human (as has happened many times throughout World history), you would (if I have understood your posts correctly) condemn them. You might even be moved to intervene. I feel that you would not be too impressed if Group A said "If you don't like it, don't participate! And do not presume to tell others how they should behave in their own personal lives." The anti-abortionists sincerely believe that a zygote is a human being. From that point of view they have every right, even a duty, to intervene. You can try to persuade them that they are mistaken but you can't tell them to mind their own business.