Natural flouride is calcium flouride. The calcium itself helps fight cavities.
Cities are using sodium flouride, which comes from aluminum production hazardous waste. There are many scientists who are opposed to articial flouridation. Follow the money.
Where do you get your information?
Here's a clue, there is no such thing as "natural" fluoride, and free fluoride ions are identical (look at the periodic table). Once a compound is put into water, a certain amount of that compound dissociates into it's component ions, for sodium fluoride, that would be sodium ions and fluoride ions. There is nothing dangerous about either the coumpound (does sodium chloride sound dangerous?) or the elemental ion.
Cities are using sodium flouride, which comes from aluminum production hazardous waste. There are many scientists who are opposed to articial flouridation. Follow the money.
Which brings up my question which you ignored, "what money?" Why in God's name would I recommend something that is going to reduce my income? It makes absolutely no sense at all.