CiG
Approximately Infinite Universe
Why does that even matter? Basically all human morality concerning human life has origin in some kind of spiritual/religious belief. That was more or less an artifact of man's limited knowledge of the world and a need to fill it with reasons to justify a given policy which would in turn support the move from tribes to more advanced cooperative societies.
It matters because I can only speak for myself and my instincts. People of different views can intersect in support of a legal standard, but via humanist ethics that I hold I come to the same conclusion as religious people on the subject of using the law to protect viable fetuses.
I didn't say these laws should be based on the instinct I referred to, just that I think with developed science giving us greater insight into the humanity of a fetus, the instinct to protect will play a greater role in changing minds. Laws protecting the fetus would exist regardless.