This ... comes from ...

Nope. This comes from the fact that when you do proper studies about overdosing (which is what you do with needless supplementation) various micronutrients you find that it is at best useless and at worst harmful. Then I added my own spin on the cause of it rather than listing studies for each chemical because I can't be bothered to write a meta study.

... if you want ... vitamin C ...

Then you should eat at least some fresh food. If you are a normal American or European you should probably also eat more fruit, but you don't need to worry about your vitamin C intake. (Unless you take more than ten times RDI ie one pill per day, in which case you should decrease your intake of vitamin C and still eat more fruit)

Edit: Based on jimrandomh's claim below I think that I should clarify that by "needless supplementation" I mean any supplementation done when it has not been demonstrated (eg with blood work at a clinic) that you have a deficiency of that particular mineral.