Quote Originally Posted by LadyEowyn View Post
However, Doylistically, I can’t see a good reason for an author to invent that.
It'd be the same as establishing any hard restriction: you would do so when your story's core question is about something derived from it, and the story would be undercut if that question was invalidated.

From the external "are the people you knew who are now a constant danger to those around them, still 'the people you knew'?", to the internal "how much is defiance of your nature worth in the cost to others?", to the expansive "if the chances of resistance change from 'impossible' to 'nigh impossible', are the world's adaptions now worse than the thing they were intended to prevent?", to the subversive "what if the truth might not be as true as expected?"; there are all sorts of questions that (depending on how the story is intended to answer them) could benefit from at least starting from a point of objective truth.