This is my take. If someone actually were to eat a whole foods diet with the USDA recommended levels of fresh fruit and vegetable consumption (5 to 13 servings per day), along with lean meats, eggs, greek yogurt, some cheese, nuts, healthy oils, and cold water fish there is no way that you would be vitamin deficient. (absent some type of intestinal disorder)
I don't think there is a problem with vitamin supplements, but rather with using vitamin supplements as some panacea for a deficient diet. We have evolved to get our vitamins and minerals that we need from a rich and diverse diet. We still do not know enough about human nutritional needs to know what we are not getting in a vitamin and nutritional supplement.
I think the opening paragraphs of the book Whole: Rethinking the Science of Nutrition, sums this up well:
"What happens when you eat an apple? The answer is vastly more complex than you imagine.
Every apple contains thousands of antioxidants whose names, beyond a few like vitamin C, are unfamiliar to us, and each of these powerful chemicals has the potential to play an important role in supporting our health. They impact thousands upon thousands of metabolic reactions inside the human body. But calculating the specific influence of each of these chemicals isn’t nearly sufficient to explain the effect of the apple as a whole. Because almost every chemical can affect every other chemical, there is an almost infinite number of possible biological consequences.
And that’s just from an apple."
Basically this means that a vitamin c supplement is a very poor substitute for just eating an apple. That said some supplements may be needed. For example, many people may need Vitamin D during the winter months. A vegan will almost always need a B12 supplement. If you run or ride a lot in the heat, it doesn't hurt to take a quality multi because you are sweating out a liter of water or more a day and small amounts of vitamins and minerals are lost when you do so (along with lots of electrolytes). Many women and some men need an iron supplement.