"Christians believe that morality and values are something that need to be referred to a higher authority, named God, who alone has the objectivity and nature to give direction."

Well, that's a nice idea, but even when this is attempted, this is not what happens. What is done is that some 'presumed' earthly representative of "God" makes a subjective judgment based on his particular religion's...and sect within that religion...notion of they 'think' God might want.....and the result is as we see - dozens of versions of 'truth' and 'right' and 'morality' all over the theological map!
It would be so easy if the were a God who parted the heavens and wrote the 'answers' in fiery letter across the sky...but...

So...given this situation, the ***ONLY*** possible answer to questions like abortion and harvesting stem cells is...If you don't like it, don't participate! And do not presume to tell others how they should behave in their own personal lives.

There IS no absolute demonstrable 'truth' about what constitutes a soul, or when it enters a body...or whather there is any such thing at all....it is a matter of personal belief....and the courts and laws need to reflect this.