One horse breaking down is one to many IMO. It sucks to have your horse scratched by the vet, but the data supporting the scratches, is pretty much hard to argue against.

How many horses have been scratched and never raced again, or where off for an extended period of time after a scratch.

I have no problem with the vets erring on the side of caution. Isn't the horse supposed to come first no matter what?