Well, we're talking about a kidnapper here. I think "kidnappers are evil" is a fairly common prima facie assumption (whether human kidnappers, dragon kidnappers, or kidnappers of any other species).
Or maybe the dragon doesn't have the capacity to realize that what he's doing is wrong?
Why? Challenge convention, I say! At the very least, we need some Anti-Villain sympathy, here. Black And White Morality is boring...
A dragon needn't think that it's immoral to kidnap a human, any more than I think it's immoral to keep a cat or a dog as a pet.
Freezair For A Limited Time
Oooh. Extrapolation from that "kidnappers are evil" idea: Though the dragon is kidnapping her from an outsider's perspective, the dragon is attempting to be nice... because life at the castle was NOT fun for the princess. The night's search to find her, and investigations at the castle, lead to a terrifying expose on the king and queen's abuse, planting the seeds of revolution...
Okay. As I said, prima facie assumption, not incontrovertible proof. There are scenarios where the dragon's innocent, or even helpful, but I think that if you're writing a story about what appears to be a kidnapping, most of the time the kidnapper is going to be a bad dude. Not always, admittedly.