I find that the argument about whether or not abortion is taking another person’s life is fairly useless ground to plow through — it’s like arguing whether or not slavery is taking another person’s labor, by arguing that the race enslaved isn’t really a “person”. The critical problem here is that once you can define away someone’s humanity, you can justify anything.
I’ve found it much more useful (as someone who, in large measure, supports a woman’s right to choose), to admit that abortion is indeed homicide, but that in some cases, it is the lesser of evils. Shooting a terrorist before she sets off her suicide bomb is regrettable, awful, and arguably evil, but when choosing between competing interests, sometimes homicide is understandable, justifiable, and granted legal sanction by our judicial system.
As horrible a person Bill Clinton has ever been, I did like his formulation of “safe, legal, and rare”. I don’t think it’s OK to kill people, but sometimes, regrettably, it is better than the alternative. I would probably support more restrictions on abortion than your average “pro-choice” advocate, but I think it’s untenable to say that we live in a world where we must never make choices between evils.
Hopefully, my acceptance and respect of your position that a zygote is human immediately upon conception, makes it easier for us to talk about how we deal specifically with the messy gray area of morality when there are regrettable competing interests. I imagine much of the frustration that the “pro-life” advocates have is in regards to the callous dehumanization often proposed by “pro-choice” advocates. I hope I’ve shown that even though I may be “pro-choice”, it is not because I am willing to dehumanize a baby before it is born — I think any decision to terminate a pregnancy should be one that fully weighs the moral and spiritual cost being paid to avoid an even worse situation.