Toothless needs to eat fish to survive though. The vikings probably did as well being as they lived in an area too harsh to support a variety of edible grains, vegetables, and fruits. Animal rights activists are not necessarily against people eating animals if there's a real survival need, but most humans living in the modern, developed world don't need animal products to survive. Everything we need to stay healthy is readily available to us in any grocery store.

The vikings in the movie were not killing dragons out of need, but because they feared and misunderstood them. Hiccup going against that was supporting animal rights even if neither of them could go entirely veg.

Just trying to clarify what I think OP meant.