I read the article and was left under the impression that we shouldn't feed our cat a diet of tuna fish. I didn't see any reason not to feed it tuna but that it may not provide your cat with good nutrition and some cats have become addicted to tuna. I have fed cats tuna as a treat for years. I don't feed them tuna if you see the difference. I guess it becomes a personal choice but my diet has many things in it that has very little nutritional value to it and I eat it. Sometimes I eat things that are unhealthy for me. Using science as a tool I can find fault with most any human diet.
Vaalerie..I agree. An occasional treat of tuna is fine. I beleive the article was based on the dangers of feeding large amounts of tuna all the time or feeding it as a main diet.
I believe that there is a high mercury level in tuna fish as well, which is too high for cats. (I didn't check the article so it might mention this.) I think as an occasional treat, a very small amount is fine though.