They raid us because they have to. If they don't bring enough food back, they'll be eaten themselves.
8 seconds sound clip from the How to Train Your Dragon movie soundboard.
You can hear this line at 01:05:24 in the Blu-ray version of the movie.
Quote context
[...]
- I screwed up. I should have told you before now. I just...
- Take this out on me, be mad at me, but please, just don't hurt Toothless.
- The dragon? That's what you're worried about? Not the people you almost killed?
- He was just protecting me! He's not dangerous.
- They've killed hundreds of us!
- And we've killed thousands of them! They defend themselves, that's all!
- There's something else on their island. It's a dragon like...
- Their island? So you've been to the nest?
- How did you find it?- What? No, I didn't. Toothless did. Only a dragon can find the island.
- Dad, please. I promise you, you can't win this one!
[...]