Remember your chemistry. Sodium is a metal that ignites on contact with water (actually it rips water apart and the heat ignites the hydrogen as I recall). Chlorine is a gas that was a weapon of war in WW I which burns your lungs out. Together they make table salt.
HCl is a strong acid, NaOH is a strong base. Mix them together and you get NaCl and H2O (salt water), possibly with a little heat (forget). Flouride is the same, F-, making an acid HF or a salt NaF.
Note: I'm not taking sides. This is simply an effort to keep minds and dialogue open.
They asked the wrong question. The better question is: Given all the other chemicals in our drinking water, how safe is flouride? Where are the studies of flouride "in the wild" in the 21st century?
Afaik, there are other First World countries that do not flourinate their water. What do those countries know that the USA does not?
HCl is a strong acid, NaOH is a strong base. Mix them together and you get NaCl and H2O (salt water), possibly with a little heat (forget). Flouride is the same, F-, making an acid HF or a salt NaF.