In a different lifetime, I would applaud this rescue for taking on this colt, and he certainly is cute.
But I assume you have limited spaces. Why do rescues take on the very sick or disabled horses when so many good ridable horses are being shipped every week? I'd really rather the spot be taken up by horses that can be adopted and don't need to ship to slaughter.
Our rescue is actually a dog/cat rescue that runs 100% on foster homes (we don't actively board dogs/cats at our vet, etc., or have a rescue facility yet), but since we have 3 horses in our family (not rescue horses), we were able to rescue Cody. The rescue has never taken in a horse before (only dogs/cats), but having a rescue and having experience with horses (blind horses too) made it easier for us to rescue him. Cody will not be at a boarding facility, but will actually end up at the horse property my family is purchasing.
Since Cody came into our rescue on a "sanctuary basis", he won't be up for adoption, so even if he can never be ridden, nobody will ever have to worry about that, as he is now guaranteed a happy and safe lifetime where he will be kept and accepted regardless of "what he can do".-- So in other words, for this very special case, our rescue would not have rescued a healthy horse simply because our rescue isn't a horse rescue per-say. So in a sense, it is actually better that we rescued him, versus a full-blown horse rescue, as now he won't be taking up the space/resources that full-blown horse rescue could be spending on other horses.
In a more general response to your concern, rescues do rescue both healthy and ill/injured animals because regardless of their situation, they need to be given a chance. It is not their fault they were allowed to get ill, injured, or were discarded like garbage from the human race.