I would not use one perhaps poorly worded question to ban all questions on the subject.
The study of genealogy or family history does not require one to be researching their own ancestors. People perform research for a variety of reasons, many of which have merit. The genealogy of royal or famous people is one of those. The fact that there might be non-genealogically related aspects to the question does not mean it is not a valid genealogical question. Why do we allow DNA questions that are really more biological questions than genealogical? Because they are of interest to some (but not all) genealogists. The same is true of royal genealogy.
Whether or not it is easy to research a particular era or place, due to the survival of records, is irrelevant to what questions can be asked. Would it be fair to ban nineteenth century questions from certain parts of Africa where no genealogical records were kept? Of course not. There are many good genealogical sources for very early medeival genealogy. One of my favourites is The Henry Project. Take a look at this site and you will see how genealogical principles can be applied, in the rigorous academic standards of this site, to early (and royal) genealogy.
Finally, I advise you to search the family trees on Ancestry.com or any other major family tree site for royal figures. A search for Henry I of England, for example, returns 264,744 family trees. Just because you may or may not believe these trees, or believe that someone has no right to claim descent from this person, does not mean that there is not a valid reason for someone to ask a question about it.