There was an ethics paper that won a student prize at oxford ..? or cambridge ..? that argued this exact position. I can't put my fingers on it right now though, it's really annoying.

edit: http://www.jpe.ox.ac.uk/papers/consistent-vegetarianism-and-...

Ethical consequentialist vegetarians believe that farmed animals have lives that are worse than non-existence. In this paper, I sketch out an argument that wild animals have worse lives than farmed animals, and that consistent vegetarians should therefore reduce the number of wild animals as a top priority.