The abortion “debate” has a simple root: what defines a person with the human right to life? In other words, the issue is really personhood.
As I don’t believe in Descartes ghost in the machine, this makes me naturally pro-choice as the issue is popularly framed. I don’t, though, support the slaughter of infant children or victims of advanced senile dementia. There are other reasons to socially define personhood more broadly:
That some people (whether for religious or non-religious reasons) tend to take a more expansive view of what is a human than some scientists desire is not a bad thing even if those people are wrong. Would you rather live in a society where the populace tends to draw too small a circle around what is human? Or would you rather live in a society where people err in the direction of greater protection?
It is certainly possible that birth is not the best time to define the beginning of “human life.” On one hand, it is far safer to define life liberally, and apply it quite early. Conception, though, I find to be unworkably early. We need to have the freedom to avoid producing children with unwilling parents, and granting a bundle of simple cells with personhood status leads to bizarre complications such as limitations on stem cell research.