People who feed Barf/raw/preymodal ect.?

First, i would never feed my dog cat food. But i am just curious.... If feeding high protein diet with meat as the main/only ingredients is best, why is it bad for a dog to eat cat food? Other than the the fact that it may have additives/preservatives/dyes etc. and is cooked (so therefore not as healthy as a raw diet), I have heard that it is too high in protien which can cause kidney failure. So if feeding a meat only diet is best, why is the protein in cat food bad? Wouldn't it be better to feed cat food then dog food as it would have the extra protein the dogs need? I was just thinking, hypothetically it would be a better choice. What do you think?