I agree completely with Maple. Its not just racing that pushes young horses hard. I also agree that the level of demand on some young started hunter jumpers is just as damaging if not more damaging then racing.
That said there are leg injuries that occur. Harness racing does have its negatives, horses do get injured and break down. It would be great if horses could not start racing until 3 or 4. I think it would also be great if weight limits on jockey's could be adjusted.
I think the horse industry is imperfect. We get in trouble when we start to make assumptions about the industry based on one or two people. This is double dangerous when you have never been on the backside of the track. Heck we have a coming 3 year old who never made a race as a two year old because he was growing. Thats not a good financial decision, to send a horse for a year of training and never see a race much less a paycheck. It was the right decision for the horse. The trainer sees that and we agree with that assessment. If this horse does not make it as a 3 year old he will come home and be broken to saddle. We will try to find him a pleasure horse home. So, please don't say that those in the racing industry don't care about their horses.
As for long term soundness issues. We have 9 horses on property. One 28 year old has arthritis in her hocks after racing to the peak and being a broodmare. We have a 24 year old gelding who has some arthritis in his hocks. He was retired at age 14 and is still upset about that. He was the king of the world at the track with people fussing over him 18 hours a day. We don't have the time to fuss over him 18 hours a day because we have other jobs. Neither horse is significantly lame enough to warrent NSAIDs or hock injections. My good mare interferes so she did not last at the track. The 5 year old was too slow, the 12 year old liked to canter, 8 year old not eligiable to race in other states due to breeding, 10 year old did not like to pass other horses, 19 year old never made it to the track due to bad hocks and traumatic leg injury, 14 year old raced but then was brood mare (now retired from that). So, where race horses end up when they retire or don't make it at the track. In my family, they end up at the house. We may not be the conventional normal; however, I know a number of racing families that do their best to make sure their retired race horses end up in good homes when they retire.
At one point, we had a horse that had been pushed to his limit. He ended up with a stifle problem and was put down as a result of that injury. His care and treatment was after winning his million dollar race, setting a track record that would stand for 10+ years he was loaded up into the trailer (not cooled off, not hot walked) and turned out in a field with a flake of hay. Once he could no longer race he was sent to slaughter where a fan of his career rescued him and then he ended up with us. His owners were not good race people. They are the kind of people that give racing a bad name.