Regarding this debate as to whether a work of fiction exists in it own separate universe, how about this as a solution: Every work of fiction is set in its own unique universe, unless, like in ST and L&O, there are several shows set within that milieu and the characters cross over, thus meaning they exist in that particular universe.
So in L&O, there is no L&O franchise, but there is a ST franchise, as well as every other work of fiction ever made. And in the ST world, there is no ST franchise, but an L&O and every other work of fiction not related to ST.
To cite just one example, we know the works of Isaac Asimov, hard sf, exist in TNG as they refer to the positronic brain concept he articulated in his robot novels and short stories.
How does that work for you all?
Red Ranger