Your brain is 60% fat and a large part of that fat is Dha found in fish and its oils. This fat can change brain composition. It can enhance cognitive abilities,fight depression,help in the treatmentof ADD..the list goes on.
fish is literally brain food.
Not to mention all the the other benefits including the production of hormones and cardiovascular health.
If you look for Carlsons Salmon oil you will find on the label that they test for Mercury and PCb's. It is excellent and they do have a great lemon flavored non-fishy tasting Cod liver oil.
I feel we do need meat in our diet for good health.
And I too do not wish to start a riot.
If someone does well on a veg/fruitarian diet then more power to them