I recently finished Anthropocentrism and its Discontents by Gary Steiner, a historical review of animal ethics. I have to say, I was disappointed. With the exception of Plutarch(a vegetarian), the historical views on the moral status of animals have basically amounted to: Don't hurt them too much while you're slaughtering them for food. Not terribly inspiring. Even Plutarch seemed unduly worried about the welfare of plants, and appears to have abandoned his prohibition against meat-eating near the end of his life.
Such a history should give us some pause, as having views that are in direct opposition to the vast majority of thinkers in human history is striking. It would be more comforting if something like an animal rights view were one of many competing historical views. The apparent uniqueness of an anti-anthropocentrist position to our point in time gives us some reason to doubt its veracity.
But, as we have seen in many other cases, humans have been slowly widening the scope of the moral community, and have had to overcome many prejudices. Given the inability of non-humans to advocate on their own behalf, we should expect that the prejudice against them would be harder to overcome. It's also not unlikely that some moral truths would be surprising to a vast majority, and we should expect that there will be points at history when great revisions are required to get things right. Now might just be such a point in history. These considerations, in light of the strength of the arguments for animal rights and veganism on their own, suggest that we should not be swayed by the historical near-consensus against such views.