Stomach pains and ulcers, diarrhea, some products are laced with ingredients found in prescription drugs. In fact, most doctors don't recommend the use of supplements, in place of a balanced diet. And plants aren't lacking? Unless you enjoy licking moss off of a wet rock, you need b12 for basic brain development and function, and no plants have that In all honesty though, saying one diet is better than the other is laughable in scientific views, because everyone's body works and reacts different chemically. What works for one person, may not for the other. It's called Anecdotal Science. If a Vegan diet works for you, great. Enjoy it. But don't condemn others based on your views.