Alright, let's break down this specific trope. That scene—Ron supposedly stealing from Harry's trunk—isn't actually from canon, right? It's a fanon invention that usually pops up in certain types of 'Independent!Harry' or 'Wrong-Boy-Who-Lived' stories. The exploration is almost never about the act itself being plausible within the original characters. It's a narrative shortcut, a very blunt instrument to accelerate a specific character derailment.
Writers use it to justify a rapid, often brutal, severing of Harry's ties with the Weasleys, particularly Ron and sometimes Ginny. It serves as the 'last straw' moment after a buildup of smaller perceived betrayals, like Ron being jealous or dismissive. The stolen items are typically sentimental: the Invisibility Cloak (his father's legacy), photo albums of his parents, or even the contents of his vault key. It transforms Ron from a flawed but loyal friend into an outright thief motivated by greed or family pressure, which then allows Harry to righteously cut him off without moral ambiguity for the reader.
What's fascinating is how it reflects a deeper desire in some corners of the fandom to dismantle the found-family narrative J.K. Rowling built. By making Ron an active antagonist through such a concrete, morally black-and-white crime, it validates a more isolated, powerful, and often darker Harry who then aligns with figures like Sirius, Remus, or the Malfoys. The trunk-stealing is less a character study of Ron and more a plot device to demolish a cornerstone of Harry's canonical support system, clearing the stage for a radically different power structure and emotional journey.
It's a divisive trope for obvious reasons. For every reader who finds it a satisfying catalyst for the story they want to read, there's another who finds it a gross mischaracterization that misses the entire point of Ron's loyalty, which was tested and proven repeatedly in the books. The exploration, therefore, happens more in the consequences and the audience's reaction than in the act's subtlety.