I think I'll let Roy explain how dragons work in (non-Eberron) D&D.Dragons, even young ones, are intelligent creatures. They can usually speak common and almost assuredly speak draconic, which makes for a very important difference between it and a cougar. Preemptively killing anything because they are "typically evil" especially when they are intelligent creatures is also evil, from the dragon's perspective their attacks against humans might be justified on exactly the same grounds. It's a very, literally dangerous associative fallacy and on top of that, it is basically racism or specisism.