The reason foridation has additional FDA requirements is because it's essentially a medicine, not a food supplement like iodine - which is an essential nutrient. So to justify the medication of entire communities at the exact same dose of a non-essential pharmacological product in an effort to ensure poor people receive enough flouride seems misguided. Calcium has a similar hardening effect on teeth and is present in water already - forming the scale you see in the shower Ca(CO3). Additionally, flouride stains your teeth [0].

[0]https://en.wikipedia.org/wiki/Dental_fluorosis