What makes vegetarians or vegans prioritize to eat vegetable is not only nutritional problems but feeling sorry for animals.
Especially, some people in Europe rallied to protest against Japan's whale hunting. Their motivation was how pity it is to kill highly talented animals. As far as I know, no one criticizes by insisting it's not better to eat whale from nutritional viewpoints.
On the other hand, for people who've avoided eating meat just because of staying health, the news would be so sad. What they have endured became in vain.
Basically, it would be difficult for general people to understand what kind of food is good for health, because of lack of knowledge on ingrediants or chemical substance. Well, it would be important to study biology, chemistry, and physics may help understand that.