The American government found it necessary to fortify cow's milk with vitamin D and salt with iodine because average citizens (who ate nonvegan diets) were not obtaining enough of those nutrients on their own.
In fact, the average omni is more likely to be nutrient-deficient than the average vegan. So... the average person isn't actually eating the kind of diet you propose. That is, by your own definition, the vast majority of meat-eaters have "something wrong with their diet."
Would you say that a person of color who lives above the 35th parallel and who therefore must supplement his diet with vitamin D at least during Winter has "something wrong with their diet"? Virtually any diet in that situation is going to require a supplement. Same goes for someone who has a fat absorbtion problem or someone who has PKU.
There are a number of situations and conditions that require supplements in order to save human lives. So why do you have such a huge problem with using dietary supplements to save animals' lives?
Sources:
Vegan B12 deficiency: putting it into perspective | NutritionFacts.org
Vitamin D — Health Professional Fact Sheet
Iodine — Health Professional Fact Sheet
Omnivore vs. Vegan Nutrient Deficiencies | NutritionFacts.org
Yes, the vast amount of typical diets have something wrong with them. I am no fan of the SAD diet, either, or in pasteurized milk for that matter. The government had to add vitamin D to the most vitamin D rich food on the planet because pasteurization removed it. But whole milk and butter from pastured animals is naturally high in vitamin D.
People of color who lived north of the 35th parallel did not need to supplement their diets with vitamin D when they ate a traditional diet rich in animal fats and fermented fish oils.
If it is your choice of diet that does not provide you with vitamins necessary for health unless you take pills, then that is not a natural, healthy diet. That is true whether you are eating the SAD diet (standard American diet), Vegetarian, or Vegan.
The Vegetarian diet does not provide human beings with vitamins necessary for health. It's not that it doesn't provide enough of them, it's that there are some nutrients necessary for human beings which are utterly lacking in a vegetarian diet. Talking about people with special health conditions is irrelevant to my point- it's not their choice of diet that requires the pills, they couldn't do without supplementation if they only changed diets. But vegetarians would not have to supplement for B12 and other vitamins (and possibly nutrients science has not yet discovered) if they simply changed their diets to a traditional one which included animal products.
There has never been a successful vegan culture. Vegetarian cultures were traditionally eating more animal proteins than they realized.
government fact sheets are generally wrong when it comes to nutrition. These are the people who spent decades telling us that margarine was healthier than butter while margarine is actually a bigger cause of heart disease- they spent decades telling us that transfats were healthier than natural fats that human beings have been eating for thousands of years. They did this because they did not know about transfats (and because they were relying on cherry picked data). But what else don't they know?
It's also not just vitamin D that's missing from vegan and many vegetarian diets. Beta Caratene is not a substitute for Vitamin A.
True vitamin A, or retinol, is found only in animal products like cod liver oil, liver and other organ meats, fish, shell fish and butterfat from cows eating green grass.
Under optimal conditions, humans convert carotenes to vitamin A in the upper intestinal tract by the action of bile salts and fat-splitting enzymes. Of the entire family of carotenes, beta-carotene is most easily converted to vitamin A. Early studies indicated an equivalency of 4:1 of beta-carotene to retinol. In other words, four units of beta-carotene were needed to produce one unit of vitamin A. This ratio was later revised to 6:1 and recent research suggests an even higher ratio.1 This means that you have to eat an awful lot of vegetables and fruits to obtain even the daily minimal requirements of vitamin A, assuming optimal conversion.
Vitamin A Vagary by Sally Fallon
Red meat is the ONLY dietary source of heart-critical CoQ10. (Dr. Sears)
Meat Protocol
As we shall see, many of the vegetarian claims cannot be substantiated and some are simply false and dangerous. There are benefits to vegetarian diets for certain health conditions, and some people function better on less fat and protein, but, as a practitioner who has dealt with several former vegetarians and vegans (total vegetarians), I know full well the dangerous effects of a diet devoid of healthful animal products. It is my hope that all readers will more carefully evaluate their position on vegetarianism after reading this paper.
Myth #1: Meat consumption contributes to famine and depletes the Earth's natural resources.
Myth #2: Vitamin B12 can be obtained from plant sources.
Myth #3: Our needs for vitamin D can be met by sunlight.
Myth #4: The body's needs for vitamin A can be entirely obtained from plant foods.
Myth #5: Meat-eating causes osteoporosis, kidney disease, heart disease, and cancer.
Myth #6: Saturated fats and dietary cholesterol cause heart disease, atherosclerosis, and/or cancer, and low-fat, low-cholesterol diets are healthier for people.
Myth #7: Vegetarians live longer and have more energy and endurance than meat-eaters.
Myth #8: The "cave man" diet was low-fat and/or vegetarian. Humans evolved as vegetarians.
Myth #9: Meat and saturated fat consumption have increased in the 20th century, with a corresponding increase in heart disease and cancer.
Myth #10: Soy products are adequate substitutes for meat and dairy products.
Myth #11: The human body is not designed for meat consumption.
Myth #12: Eating animal flesh causes violent, aggressive behavior in humans.
Myth #13: Animal products contain numerous, harmful toxins.
Myth #14: Eating meat or animal products is less "spiritual" than eating only plant foods.
Myth #15: Eating animal foods is inhumane.
Further information is given about each of these myths at this link:
Myths of Vegetarianism - Weston A Price Foundation
Another problem with any diet heavy in grains is the phytic acid in grains and legumes. If these foods aren't prepared properly, they are binding to minerals in your digestive tract and rendering it impossible for you to benefit from those minerals. This is not limited to vegetarians, of course.
Preparing properly includes soaking and rinsing, soaking in a light acid, or sprouting, or fermenting.
Sprouted bread | The Sweet Beet
Dr. Weston Price traveled the world to study indigenous cultures and find out what their diets were like. He fully expected to find that vegetarian cultures were more healthy, but that is not what he found. He was disappointed about it, but he reported the truth about what he found.
Also see The Omnivore's Dilemma by Michael Pollan; Folks, This ain't Natural by Joel Salatin; Mary Enig's works...