I'm against it, unless it's the only way to save a woman's life, such as in an eptopic pregnancy. In that case, you'll lose one life or you'll lose two, and you save the life you can. Generally speaking, you do whatever you can to save the lives of both the mother and the child.
Why am I pro-life? Primarily, it is because it is self-evident that an unborn child is in fact a person. And morally, every person has the right to life unless he or she has forfeited that right by becoming a murderer or a rapist or something else on that level.
If I were an unbeliever, none of the above beliefs would change. If I were a pro-choice unbeliever (and I'm not projecting this on anyone else, I'm just talking about how I would justify it), I would simply not care about the unborn child's rights. I would just believe that it's in the way, so too bad. And I may dabble in some of the pro-choice arguments, but that would be the soul of it, since they don't really hold water and I would still see that. Then again, I'd probably be more of an advocate for vigilante justice too, just to give you some context of the kind of person I'd be. I'd be an all-around culture of death person.
Now, Biblically, there are a couple more things:
"You shall not murder." - Exodus 20:13
"For you created my inmost being;
you knit me together in my mother's womb.
I praise you because I am fearfully and wonderfully made;
your works are wonderful,
I know that full well.
My frame was not hidden from you
when I was made in the secret place.
When I was woven together in the depths of the earth,
your eyes saw my unformed body.
All the days ordained for me
were written in your book
before one of them came to be. " - Psalm 139:13-16
God is working on every one of us and has a purpose for each of us, even if a person or people can't see it. He has a purpose for the kids born with physical and mental birth defects. He has a purpose for those born from less than ideal encounters. And for that reason, they have value and deserve protection. Having an abortion is interrupting God's process of forming a life. Most of us wouldn't mash a pot that a potter is throwing on a wheel, even though it is and will continue to be an inanimate object. How much more should the Christian and the Jew have respect for human life that God himself is in the process of making.