Oh my gosh, I've had this same conversation so many times over the last 25 years. Here's what I've learned...
Those people who enjoy excellent health see no need for taking vitamins. With the exception of Vitamin D, they are probably right and I respect their decision. However, if they are eating a vegetarian diet, that's a different conversation. In that case, supplementation with specific nutrients is needed. And if you want to argue about that, take it up with Michael McGregor, M.D., not me.
However, when those same people take the stance that no one needs nutritional supplements I have a
big problem with that.
For those of us who have gut issues, and there are a lot of us out there, or circumstances such as eating a poor diet for years, or conditions that lead to specific nutritional deficiencies it's not that simple. (Nor is fixing those issues, particularly gut issues).
In an ideal world, those who don't feel well should be checked for nutritional deficiencies, but here's the problem, it's expensive - (here in the US, I have to pay $75 to get my vitamin D level checked; insurance doesn't pay for it) - not everyone can afford it. If on the other hand, you can afford it, I think it's a good idea.
I have taken nutritional supplements off and on for 25 years. And thank goodness I have because I don't absorb nutrients well from food as evidenced by multiple nutritional deficiencies when I was tested in 2011. It took me a long time to pay off that bill.
Common nutritional deficiencies are the B vitamins, D, and magnesium. Vitamins are synergistic, so taking a good quality multi-vitamin is a good idea.
For those who have chronic health conditions and don't feel well on a daily basis, I know of no harm in taking any of the above listed vitamins, so long as they are of high quality, and are well formulated, unless the person is taking high amounts. Vitamin D levels however do need to be checked because there is a therapeutic window, both low levels and high levels are problematic. I personally eat a healthy diet and I take nutrition supplements primarily made from organic, whole foods.
I think it's fine to have opinions. Please keep in mind, that what works for you may or may not work for me. I respect your decision to not take nutritional supplements. However, offering general advice can help or harm, particularly when the advice is uninformed.
I'm leaving the house soon, but if you have any questions or a need for clarification, please ask. I'll respond to any reasonable requests for information.