What Christopher said is (bold added by me):
I'm talking about telling a story that could not be told without the scientific concept in it. "Tuvix"'s powerful ethical and personal dilemma couldn't be told without the science-fiction conceit of a technology that can combine two people into one. Without the science, the story wouldn't even exist.
I'm saying that the science isn't the important part. It can be told in other ways, magic, for example. Tuvix isn't a story about the technology to merge and separate individuals, it's about the moral and ethical actions that you do or do not take. How they got merged is irrelevant.