The aim of the water fluoridation programs isn't to "add" fluoride willy-nilly - it's to *standardise* water supplies at the 1mg/L which is around the most common naturally-occurring level, and gives the most overall benefit.
Oh, and if you want to classify fluoride as a "toxic chemical", fine. Just be aware that, in order to be consistent, you'll need to also classify sodium, chloride, calcium, magnesium, potassium and iodide as "toxic chemicals" too. They're all in the same class: naturally abundant monoatomic ions found in varying concentrations in every water body on earth.
Fun fact: did you know that fluorine is actually far more abundant in the Earth's crust than chlorine? The only reason that there isn't far more fluoride in the water is that fluoride compounds tend to be somewhat less soluble than their chloride equivalents.
