Speaks for itself...
This is true. Sodium flouride is a by product of aluminum production, I believe. The aluminum industry used to have to dispose of it as hazardous waste.
Then, someone noticed that people in some community had an inordinately small number of dental caries (that's cavities to you victims of the public schools). The aluminum industry was able to sell the idea to our politicians that adding this dangerous chemical in small amounts to the public drinking water would prevent dental health.
Whether or not flouride contributes to dental health or not, there are other considerations. First, what is the long term effect on the various organs of the body? Are some individuals more likely to develop a reaction to it? And most of all, where did government suddenly get the authority to force medicate?
Some people point to the use of chlorine in drinking water. Chlorine can also be deleterious to health, but chlorine is used as a disinfectant. So, there is a trade off. Chlorine make the water safe for consumption - with the possibility of long-term negative effects. This is acceptable, because it is the safest method. Using a dangerous chemical in small amount because some people believe (or were paid to believe) it is beneficial is a different story.