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.

Bayes disagrees with you.

If you know that most people in your country (the United States for example) are deficient in vitamin D then prior to having blood work done, and absent any other evidence you have collected that suggests you are an exception, you should expect to be deficient in vitamin D.