Yes there are many opinions on dog diets. Some of them are based on controlled, scientific feeding studies, and the health of thousands of dogs like the dog guide program I am very familiar with where the dogs are eating Pro Plan. Same thing in many other programs I am less familiar with, feeding Iams or other conventional dog chow. Even in service dog schools' breeding programs, the only special diet is puppy chow for pregnant and nursing mothers.
Some are based on little but speculation, junk science, and anecdotal evidence.
Junk science is Aristotle speculating that heavy objects fall faster than lighter ones. Everybody believed that until Galileo lugged those balls up the tower at the dawn of modern science. Real science confirms its theories with testing.
Dogs aren't wolves. It is well accepted that sudden changes of diet give dogs diarrhea. Apparently wolves manage better. Of course, for an animal that is free to withdraw from the den anytime, diarrhea isn't as much of a problem.
It is easy to show many dog chows contain corn and find websites condemning it. What is harder to find, is a site with real evidence that there is anything wrong with corn. Yes, it is true that many dogs do develop allergies to corn. Dogs aren't born with allergies, although perhaps genetically predisposed to developing them. If barley, millet, or some of the other less common, highly touted ingredients were as common as corn, likely they would be just as big of a problem. Best to start a dog on a common protein source and stick to it, so if it does eventually develop an allergy, there are plenty of alternatives it wasn't exposed to.
You can find a website backing almost any opinion. You need to look at who is behind the website. It may be some non profit organization with a nice sounding name, but maybe funded by somebody selling specialized dog chow including frozen BARF. You have no idea of the financial interests of those posting to a forum either. I have been accused of working for Purina. If I did, if my boss ever saw all the things I post supporting Pedigree, Iams, Science, etc. I would be in trouble. Not to mention all the time I spend helping with behavior problems, housebreaking, crates, and trying to discourage irresponsible breeding. That is an important issue, and I am disappointed how little support comes from somebody calling herself the Animal Advocate.
When it comes to who backs or opposes what, I frequently give links to the American Veterinarian Medicine Association. I trust them much more than unknown organizations. Go to
American Veterinary Medical Association and do a search on raw. You will find out the federal government has condemned the raw diets for dogs, not because of the dogs' problems, but because the increased handling of raw meat is giving people food poisoning. All the people pushing raw diets never bother warning people to use good sanitation.