Fallacy for asserting conclusions from constructed assumptions (fiction)

What fallacy best suits deriving a conclusion about the real world from a set of fabricated assumptions, in the case of a piece of fiction, or possibly a set of assumptions fabricated for the sake of an argument that are meant to model the real world but the accuracy of these assumptions is dependent on the arguer's ability to simulate the real world in their assumptions. Ultimately this seems to be a case of presuming assumptions that have the possibility of reflecting reality, but I'm not sure how well it matches up to well-known fallacies.

There are some points about the question which I'd need to see clarified so that it seems more objective and less "loaded".

I think most issues of reality are quite complex and that arguments meant to address them or it, do so by simplifying, and use analogies.  The question then becomes one of accepting or rejecting them as "apt", or adequate for the purpose of logical analysis.

In terms of the current question, the loaded terms "fabricated, fiction" bring the possibility of intentionally misleading assumptions.  If the argument starts on such a basis, it probably can't be continued.

If the original question was not intended to include the implication of intention we are left with the usual possibilities for logical analysis, which in civil discourse will benefit imo from taking the time to reach agreement on the analogy's aptness.

Such agreement-reaching might in fact be the sum and substance of the discussion.