Horses are being breed for our entertainment and also dying, other animals are being breed and being experimented on for research on drugs. Where do you draw the line ?
There's a world of difference between breeding animals to be experimented on and breeding a race horse.
I am totally against animals used in experiments or even being browbeaten into performing tricks but race horses are extremely well looked after and are bred to do something they enjoy doing, running. The terms 'free rein' and 'reining in' come from horse riding, the former allowing the horse to go at it's own pace and the latter slowing it down.
Yes it's unfortunate when a horse dies but horses can injure themselves when in the field grazing.
Edit.
Forgot to add, if a horse didn't want to run it would stop when the jockey fell off but they keep going.