Good dragons under the control of bad people do bad things.
Read more Valka QuotesFrom: How to Train Your Dragon 2 (2014)
Hiccup : This is Berk. A bit trampled and busted and covered in ice, but it's home. It's our home. Those who attacked us are relentless and crazy, but those who stopped them - oh-h-h-h-h, even more so! We may be small in numbers, but we stand for something bigger than anything the world can pin against us. We are the voice of peace, and, bit by bit, we will change this world. You see, we have something they don't. Oh, sure, they have armies, and they have armadas, but we... we have...Hiccup : ...OUR DRAGONS!
May the valkyries welcome you and lead you through Odin's great battlefield. May they sing your name with love and fury, so that we might hear it rise from the depths of Valhalla and know that you've taken your rightful place at the table of kings. For a great man has fallen: A warrior. A chieftain. A father. A friend.
Now dragons used to be a bit of a problem here, but that was five years ago. Now they've all moved in. And, really, why wouldn't they? We have custom stables, all-you-can-eat feeding stations, a full-service dragon wash, even top-of-the-line fire prevention, if I do say so myself.