Over the weekend, I noticed this question about why dragons would be afraid of fire. To me, it seemed like a pretty clear-cut case of an opinion-based question. There are currently 17 answers, each of which seem to be equally valid. There isn't enough information provided in the question to constrain answers, or to provide any indication on what the OP is looking for. There isn't even a solid definition of the OP's dragons (how big are they? Are they intelligent? What natural defenses do they have?). In fact, even if it's not 'opinion-based' (maybe I'm combining that close reason with the retired 'idea generation'), then it's still definitely too broad.
Despite this, everyone who reviewed my VTC chose to leave the question open. I don't review that often any more, so maybe I'm out of touch. Can someone explain to me why I'm wrong, and how that question was suitably constrained and not opinion-based?