Ah fuck this. I'm gonna rant.
From a liberal Christian perspective;
There is no questioning the sanctity of life.
But the bible doesn't get too specific about alot of stuff. Including at what point life occurs during the union of man and woman.
Moreover, God gave us the talent and faculties to explore science. He also gave us the reasoned judgement to determine right and wrong (or we took it rather; but now we have it and we must use it).
For God, he detests handing out talent... and then having it wasted. But isn't that what this knowledge is? A talent to humans, that we're willing to waste as we bicker and spout rhetoric about the sanctity of newborn life...
while ignoring the sanctity of living life?
To me, it's not even a question... the stem cells needed come generally during the blastose stage of birth; at this point, the cells are present and they're dividing and making more cells. At this stage, they're essentially a collection of divisible cells. Although the potential for life as we understand it resides in those cells, they're not living humans.
Consider the foundation of a building. Although it is the start of a building, it cannot be called one. It is in essence, a concrete slab. At this point you could change it into a carpark and not have lost a building.
At some point during the construction of the building, ontop of the foundation... you *can* call it a building, though unfinished.
Similarly with human cells; the blastose of cells can be used for other things at this point. Up until this point in time, we've never had the talent to exploit its use for anything but the growth of human life. But now we know; like a foundation, they can grow into life; but aren't to be considered human life in and of themselves.
If you don't take the time to understand how life works, but instead openly voice in ignorance opposition... then it is a mortal sin. Not only of ignorance but waste (of a talent).
I don't think any reasonable person can argue that the locus of our life is our brain; in it, our personality, and everything else that makes us more than just a cadaver resides. If you believe in it, then it is also the home of your soul in your body.
At some point during development, the blastose of cells will begin to mark groups of cells as bone cells, muscle cells, heart cells and neural cells. Neural cells alone don't mean much... but eventually they form a cluster where a network of activity can occur. At that point, I think a fetus can be considered 'living'.
But to be on the safe side, because we know the development of human life can be variable, we give a leeway and say that the sanctity of human life occurs at X amount of time before the actual expected development of the neural cells.
But even with that, we can readily expect to use the stem cells we need; preserving the sanctity of new born life while solving the problems that God has given us talent to do so; in turn giving new meaning and preserving the sanctity of current life. To do less, would be a grave sin, now that we know better.