For example if you claim to prefer non-existence of animals to them being used as food, then you clearly must support destruction of all nature reserves, as that's exactly the same choice. And if you're against animal suffering, you'd be totally happy to eat cows genetically modified not to have pain receptors. And so on. All positions never taken by any vegetarians.

I think most animal-welfare researchers would agree that animals on the nature reserve suffer less than those in factory farms, where conditions run contrary to the animals' evolved instincts. As far as consistent vegetarians, I know at least 5-10 people (including myself) who are very concerned about the suffering of animals in the wild and who would strongly support genetically modified cows without pain receptors. (Indeed, one of my acquaintances has actually toyed with the idea of promoting the use of anencephalic farm animals.) Still, I sympathize with your frustration about the dearth of consequentialist thinking among animal advocates.