I get that. I do. But the film never explored what function the Queen Dragon (I like that :)) had in their society. Did she lay all the eggs? Have they doomed their species to extinction with her death? Will another dragon rise to take her place? I get the necessity of having a bad guy for storytelling purposes — for a while there, Hiccup’s father fit that role, but they couldn’t reasonably vanquish him, so they brought in another big bad that could be killed instead.
All I’m saying is that even the scary dragon who set himself on fire was just a scared animal, who reacted with curiosity to an outstretched hand. Obviously the communication difficulties with such a large dragon would be daunting, but no one, not even Hiccup, ever even attempted to find an alternative to killing it. The scope of such moral ambiguities is understandably beyond a children’s animated film, but why introduce it as a story element at all when the solution completely countermands the underlying message of the entire film?
Basically, what it comes down to is that taking the time to understand things you don’t understand removes the need for violence, unless the thing you don’t understand is especially big and scary, in which case you kill it.