I've never had any interest in horse racing. Is it cruel? I honestly am not sure. If it is then what about the use of horses for riding by man under any circumstances? If one truly believes in the rights of animals why is it a "limited" right? e.g. it's fine as long as they're not "mistreated". In what way does a dog, cat, rabbit or horse have it's rights infringed because of being kept as a pet by humans? Why are people not against that in principle, rather than feeling humans have a right to enforce animal behaviour to their will, as long as the animal is not being mistreated? Is not just the act of keeping a dog as a pet a mistreatment? The dog would not of it's own free will, if born in to the wild, decide to spend it's life mostly locked up in someones home/garden etc.
Also I strongly agree, the equivalence with the Cambodian Killing Fields is outrageous.