'a materialistic sophisticated Christian'
I liked the dialog you wrote but it seems strange that he still judges based on the soul when he's sophisticated and materialist ,:-. though MS seems to have his own idea in mind that I didn't think of at least. Also didn't the sophisticated Christians in the Vatican say aliens could have souls so "human" as criteria seems more restrictive than them. Just my thoughts it's your character just might be worth updating small details of your Christian model if I'm right :)
A few years ago, I wrote a little dialogue I imagined between 2 materialists, one of whom was for and one against abortion, centering on the personal identity question. I recently cleaned it up and added a number of references for the biological claims.
You can read it at An Abortion Dialogue.
Early feedback from #lesswrong is that it's a 'nicely enjoyable read' and 'quite good'. I hope everyone likes it, even if it doesn't exactly break new philosophical ground.