Well, it may not be the healthiest possible thing to do with a horse, but not a single equestrian sport is over a certain level. Riding may not be the healthiest thing for my body physically either, its stressful on the knees and hips, and dangerous.

No horse lives forever, and they enjoy it as much or even more than we do. Why argue over whether or not its "natural" or "cruel"? A horse with drive like these jumpers, they would go nuts without a job.