This letter from Portland mayor was obviously ghost written for him by Delta Dental or the oral health division of the CDC.
The evidence cited does not prove the assertions made. Follow the links and you just see more conclusory statements.
Also there is nothing about the fact that fluorosilicic acid contains lead and leaches lead from pipes and fittings.
There is nothing about diabetics, athletes, and workers who labor in the sun and who drink ten times as much water as the sedentary worker. A small amount of fluoride, lead, arsenic, and hydrogen fluoride is not okay.