I am sure you know that vets that spay an animal are doing it for the best health reasons for the pet.I guess maybe you have different roosters over there, but here ours crow at ALL hours. At night is the only time mine did not crow. I guess vets that spay are only in it for the money also right?
If they don't have this operation they can get cancer, or other life threatening illnesses.......the operation dramatically reduces or totally get rid of these potential illnesses. Its a great advantage to the pet, and also help to stop the massive number of unwanted puppies and kittens.
Now this is TOTALLY different from de crowing a rooster. This has more dangers to the bird, and NO health reasons to do it. There is also not a massive overpopulation of unwanted and stray chickens, so that need is no there either.
I don't know how anyone could compare the 2 things really.