If you're careful on how you start a young race horse, you can actually strength the bones and tendons, as they remodel to handle the stress as they grow. The problem comes when racing (or any) trainers are in a hurry (or unaware) and skip steps, which can lead to breakdowns, bowed tendons, and bone chips. Not ALL off the track race horses (STB or TB) are broken down or have life-long injuries.
Now, it would be a lot better if the first race wasn't until 3yrs old. That would give the horse another year to grow and prevent injuries from trainers that hurry or don't know about properly conditioning a young horse's bones. However, racing at 2 can be done without injury if done right, AND if breeders would bring in a little more strength instead of just speed... (but that's another discussion entirely, lol)
Mmm, I would say you're partly right. A lot of these injuries with the babies are not because trainers are in a hurry (though some are I will say that) but also because they are underdeveloped. Joints are still open and they are still growing. If you look at the statistics (im not 100% sure on the percentages so I wont claim any certain percentages) less than half of the foals born will make it to racing as a 2yr old, either because they break down, or are just not fast enough. I mean, im totally sure its not safe to be racing a 2yr old. And unfortunately these days with the drugs that are on hand and the breeding that these horses are getting, its all about speed. Races are going faster and faster, and the demand to keep up... well... lets just say now-a-days racing is more "chemistry" than training
its sad, but that's just how it is now. Horse A and B can be completely even horses, but if horse A has better drugs than horse B, horse B just doesnt have a chance, no matter how good the trainer is.
And as far as why we race 2yr olds, well I personally never have. Our first 2yr old didnt make it, she bowed a tendon. And not from training or anything, it was bad blacksmithing... they took off too much foot in one shoeing and she bowed because of the drastic change of angles. Anywho she's off for the rest of the year and will come back as a 3yr old. We do have another baby who will be broke soon and start training to race as a 2yr old. I don't do it because I think its wonderful, I do it because I have to survive. There isnt much money is harness racing anymore, it TB there is, but not STB. The money is all with the babies, 2 and 3 yr olds. And unfortunately a lot of the 3yr olds you have to complete against have raced as 2yr olds and that makes them more advanced, they know how to race, they arent green. Its hard to race a 3yr old that's never raced before with others who have, they have a great advantage there.