Do vegetarians suffer mental problems ?

It seems alot of humans pretend to be vegetarian, and since mankind has been eating meat from stage 1 , why do people "choose" to be vegetarian ? and is it possible that it could cause problems with the brain due to a lack of essentials which we can find in all meats ?? it has become clear to me that vegetarians like to say something like , " it was a life form, i don't want to eat it", as if vegetarians are alot more concerned about life than meat-eaters, but its a well known fact that Adolf Hitler was a drug free, yes, drug free -> vegetarian.