The author manages to contradict himself with the final statemenst about there being many good reasons to go vegetarian or vegan when he just wrote a great expose detailing why going vegan or vegetarian would have made us all puny idiots. If going v and v would have made us inferior now, it will then make us inferior in the future. Moral of the story: to stay strong and smart, eat meat.
The author of the article is a science writer, not a scientist, expressing pure opinion with that statement.
People try pure vegan diets, but I have yet to hear of someone sticking with one permanently. There also isn't any research establishing that such diets are actually healthy. Nor is there any scientific reason to believe that vegetarianism is somehow better for the environment. I know that there is a lot of hype claiming scientific support for these assertions, but reading the original science articles reveals that the scientific basis isn't there.
In the early 17th century, the Sikhs switched their policy from pacifism to armed resistance against Muslim oppression.
To further this switch, although they had previously been vegetarians, they were instructed by their Guru to eat meat so they would grow strong.