Making up a situation—without disclosing that it is fiction—is risky in a practical sense and also morally questionable.
Readers typically don't like to be deceived when reading non-fiction. If a specific detail is fabricated and a reader notices, a reader can assume that the writer is sloppy/deceptive, and become far more skeptical with the rest of the author's works. Undisclosed fabrication can also lead to unsound conclusions (for example, an article could rely on the existence of a counter-example to disprove a rule, but a fabricated counter-example would make the argument fail to be valid).
Furthermore, suppose a reader cites an article with a fabricated story, relying on that story to make a point. If the story is false, the reader would take a reputational hit as well. In a moral sense, it's better for the reader to avoid fabricating situations.
It is typically good practice to make an article introduction easy-to-understand with minimal jargon, but creative license should always be disclosed when writing about a hypothetical situation. It leads to higher-quality reasoning (by avoiding arguments that rely on false anecdotal evidence) and is simple to disclose (e.g. "Consider a hypothetical: ...").