Hi doma,
"Harvard University researchers' review of fluoride/brain studies concludes "our results support the possibility of adverse effects of fluoride exposures on children's neurodevelopment." ... "The children in high fluoride areas had significantly lower IQ than those who lived in low fluoride areas," ...
"However, they point out research by Ding (2011) suggested that low water fluoride levels had significant negative associations with children's intelligence."
Ignoring the attorney, my initial interpretation of the message is: not too much, not too little, but just right.
My interpretation of the whole conversation: fluoride has effects on people. Some of these effects are good and some not so good. The strength of the effect depends on concentration.