A top-performing horse like Eight Belles has a great future, for breeding as well as racing, and no one on her team would have let her start the race if she had any indications of injury, or to continue if she was hurt during the race. I'm not an expert--these are just things I've picked up from years of reading and talking to people who are. I think PETA is just grandstanding.
PETA is a few rungs lower on the evolutionary ladder than J. Fred Muggs.