I think the argument the original poster is trying to make is: statistics say people that eat fish are more healthy, but this is because of certain components of fish (like Omega 3s) and not something only providable by fish. These other sources (like flax seeds for omega3s) aren't shown to have large amounts of toxins. However, because it takes a variety of alternative foods to get all the healthy components in fish - even though an individual will be better off doing that - it would be hard and complex to find enough individuals eating all the healthy things combined to statistically show it's healthier then fish.

What argument, who's arguing? I'm saying that making decisions for your own particular situation based on what would happen to population statistics is fairly tricky.

Especially because of the epidemiological nature of these studies, lack of interventional studies for this particular subject and a bunch of other completely logical reasons.