https://vegan.com/health/protein/

"Diet For a Small Planet, however, unfortunately helped create a persistent myth that vegetarians and vegans faced severe challenges when it comes to getting enough protein. Over the next few decades, multiple studies coupled with the lack of vegans dropping dead from acute protein deficiency extinguished that hysteria."

It takes like .2 seconds to verify if your sincerely held religious belief is utter nonsense or not.

Maybe that's why so few people bother learning.