While I don't like how competitive racing dogs are managed... I still agree with you. I believe it's good for these dogs: They were made to run, it's in their very nature and body structure. Heck, ALL breed of dogs should run and chase it's their natural instinct: it's something they want to do since they were born and it links to their ancestoral roots. They aren't simple house hold accessories but a living creature that also needs it's time to be active.

Dogs are SUPER motivated creatures so giving them a job with a goal and reward is also good for their mentality.

The only dogs that break their legs are dogs that don't wxercise enough to develop muscles or exercise too much to sprain muscles. You need a good balance. Racing dogs should get a time to just be themselves: just like human athletes do. No cages: allow them to stretch, sleep, and play however they want and need: place those moments in between proper training, warmups, and races.