Horses are all about movement. Thoroughbreds are all about speed. Horses being prey animals are built naturally to run fast enough in short bursts of speed to get a far enough distance away from a predator. The thoroughbred has been bred over hundreds of years to build on that trait (and stamina and strength) like a kind of speeded up evolution. Imho, there is nothing unnatural or wrong about an animal doing what it was bred to do.
If a thoroughbred with its enormous heart and lung capacity and capacity for speed (those of you on here who have ridden one know that they are usually very keen to run; you are usually holding them back, not slowing them down!) ) cannot race; it simply will not exist.
Welfare standards in British racing have never been higher and huge efforts are being made with regard to the retraining of racehorses post retirement; see some of the activities listed here.
So yes, the horse racing is an industry and an entertainment business. But there is so much more to it than "horses being made in to an entertainment spectacle". Huge skill, time, money and effort goes in to the breeding, schooling and training of racehorses (not to mention massive amounts of manual work, 365 days a year, 24/7 in all weather conditions). And never before has so much trouble been taken to ensure that the quirks and preferences of individual horses are taken in to account.
And as with all sports only the creme de la crème of jockeys, trainers and owners make money from it and even then there are lots of ups and downs. The vast majority of people involved are doing it for the love of the game. In fact, given the hard work and commitment involved, you'd be mad to be involved if you didn't love horses!
I am pretty sure that there would be many people upset by the horse's death you witnessed op. The trainer, the owner, all the connections and fans and admirers of that individual horse, and not least it's lass or lad who would have been travelling home in an empty horse box which is a soul destroying experience.
Racing people are generally down to earth and not given to excessive sentiment. But, speaking as someone who is involved in a tiny way (part ownership/member of syndicate) that doesn't mean that they don't care.