Of course a person's decisions will be guided by their faith, but I never hear arguments against abortion that aren't founded, in some part, in religion, and if an argument does not have a basis outside of a specific religion I can't find it valid.
I wish there were a good litmus test for this.
Let me give you one (and mind you, I'm pro choice) -
Ignoring cases where the health of the mother is at risk, let keep it simple, I'm walking about termination due to unwanted pregnancy.
So I hope we can all agree that killing the baby 5 minutes before it's born during labor is bad, right?
And we can all agree that using a condom isn't murder.
So that mean that sometime between conception and 5 minutes before delivery, there's a point where the fetus start being a human being that deserve protection.
Now considering that conception is the most significant epoch in pregnancy (or at the very least the most easily identifiable) and since you'd rather err on the side of not killing people, wouldn't it make sense to say that life begins with conception?
Now to be clear, I'm not just playing devil's advocate for the hell of it, I honestly think it's a difficult moral question, one that I hope I never have to face (especially when you deal with a pregnancy that is a bit more advanced), and one that new scientific discoveries can change my mind about.
Personally, I support abortion rights because I believe that forcing a mother to carry a baby she doesn't want to term is a bad policy that yield bad results for everyone. I still believe that as a society, it's better to try to reduce the number of abortion (mostly through sex education and contraception).
And I really hate that we break automatically along party lines on it.
p.s.
The religious argument is mostly shit though, the bible doesn't talk directly about abortion, and from it says about pregnant women it's easily to infer that a fetus is a not a human being than the opposite.
Edit:
AGHHHHHHHHHHHHHHHHHHH!
forget everything I said, abort everything and everyone, coathangers this shit from orbit, it's the only way to be sure.