The issue has not been the positive effects of fluoride in the water but rather the negative effects of fluoride in the body. For example, a study conducted on a population that consumed excess natural fluoride showed that...

"Excess amounts of fluoride ions in drinking water can cause dental fluorosis, skeletal fluorosis, arthritis, bone damage, osteoporosis, muscular damage, fatigue, joint-related problems, and chronicle issues. In extreme conditions, it could adversely damage the heart, arteries, kidney, liver, endocrine glands, neuron system, and several other delicate parts of a living organism, briefed in the present article."

The key word in this study was "excess" amounts of fluoride. While water companies are pretty good at controlling the amount of fluoride in the water, they can't control whether people are getting additional fluoride treatments at their dentists, using fluoride toothpaste, rinsing with fluoride mouthwash, etc. Nor how individual's bodies react to excessive amounts of fluoride due to impaired kidney function as an example.

All of which suggests, that simply saying that public drinking water should be fluorinated may in fact be too simplistic. Instead, in order to secure the benefits of fluorine without creating other health issues, we would have to have a means of determining and addressing the health issues of those that should not be drinking fluorinated water.