Here is the reaction for the Humane Society of the United States. Although I'm not sure if I agree with everything in the post, at least he is using it as an opportunity to comment on the industry as a whole and the realities of the sport. A much better way to approach it, in my opinion, then how PETA is handling the situation.
"The tragic death of Eight Belles, as discomfiting and disturbing as it was, is unlikely to reorder our priorities. We'll say a few words about horse racing, as do the commentators and industry press, but we'll return to our priorities in a couple of days. But that's a mistake for us all. This industry has not had a rigorous critic to set it in the straight and narrow, and major problems have grown and festered. It's time for the thoroughbred industry to deal with its problems, and if it does not, animal advocates may well decide they can no longer continue to give the industry a free pass."