Exactly this.
From a mod perspective:
Nearly any topic can be expanded: a topic about a specific issue of bigotry, for example, could be expanded to ask about similar issues, issues affecting other races, even semantics of the term itself.
Because of this, the mods narrowly define topics when they are derived from Boing Boing posts.
Suggesting that a discussion about a movie involving transgender themes expanding to encompass every possible situation an actor could act in, for example, has nothing to do with the Boing Boing post. Worse, because the expanded topic essentially has no boundary, the now-expanded topic completely derails the narrowly focused discussion surrounding the original post.
Now, a great thing about Discourse is: any established user can split a topic off into a new one - if you want to discuss the plight of actors acting in a world where roles are given to the cultures, races, or lifestyles of the people actually portrayed, for example, then feel free! But understand that broad, overarching topics tend to be very difficult to follow in an online forum format.
