[user104658]

Honestly even if you argue that it's in their DNA to "run with the herd" which it probably is and they undoubtedly get enjoyment out of that behaviour, I don't think anyone can possibly argue that it's "in their DNA" to jump over large obstacles as part of that and it is ALWAYS on the jumps that horses are injured or killed. The hurdles exist specifically so that some horses will fall, to add to the excitement, despite them being dangerous for both the horses and riders. There's no real justification for it.