When a culture still has to deal with the reality that one predator can starve an entire family, eat family members, or simply ruin all the work they put into their farm/hunting/gathering over the course of the year, the dragon, the wolf, the unnameable beast is simply and easily the villain.
The western dragon especially is often seen as the personification of all the fatal dangers that northern tribes faced. Snakes, cats, wolves, eagles, and fire. Dragons were the villains in old Eurasian folk tales for the simple reason they were everything that would kill you quickly and painfully.
However as cultures pulled away from the days when the wolf would literally come to your door the mental image of dragons softened and changed.
Most recently there seems (to this author at least) to be a shift towards depicting them as the embodiment of logos, of truth in the spoken word. Perhaps the most mainstream example of this is in the DC comics JLA: A League of One, wherein Wonder Woman has to fight a corrupted dragon alone. This falls to her not for her superior strength but because of her dedication to the truth as represented in her lasso. (Granted the writing is a little odd given that the near absolute truthfulness of Wonder Woman is the crux of the story but she also deceives the entire JLA in the story.)
Sometimes the fire burns the deceitful and leaves the honest, sometimes the light in their eyes responds to the truthfulness of their challenger.
My own dragons have quite the flavor of logos about them, which was not something I intended when I began to write them. It just happened.
So here is my question.
When did the cultural zeitgeist whisper that dragons are logic, truth, and reality without compassion?