fenwoman, just been looking at this site regarding pet food here . Maybe I was wrong regarding diseased animals (officially), but certainly wouldn't want to feed too many cheap by-product related food to my cats. I think you are wrong regarding some of what you say about pet food. Most cheap cat foods do not contain muscle meat for taurine, the taurine is added because it is lacking in the food and destroyed in the manufacturing process.
Dry food alone is not a suitable diet for a healthy cat, and just because a cat appears to be doing well on a dry diet does not mean it always will or that all cats will. A cat may appear healthy for years on a dry diet, until it gets diabetes at 14 years old, or even 18 years old, or is slowly and silently developing kidney stones or kidney disease.
Also, all dry foods are not the same quality- for instance go-cat has grain listed as the first ingredient, and there is only about 20% of that so must be far less than 20% meat. Yes, all pet foods have to contain a minimum level of protein, but it doesn't have to be animal protein, if you think your cat can live happily on vegetable protein then, fine, some people think their cat be vegan!
Yes, you need to read the labels as expensive doesn't mean better, but not all cat food is created equal.
If you want to feed a good food, then hi-life puches with 60% meat from the supermarket is about the best. I feed my cats from www.zooplus.co.uk/shop/cats and buy Grau, Smilla, Bozita,
naturesmenu.co.uk/products/Pouches_for_Cats/Cat_Food_Pouches/ is also a good food and available at most large pet shops such as pets at home or jolleys.
There is lots of advice here about feeding cats and many very knowledgeable people. www.petforums.co.uk/cat-health-nutrition/