The link above is not reputable and was directly refuted by, among others, the American Dental Association, the American Dental Education Association, the American Association for Dental Research, the American Academy of Pediatrics, and the Harvard School of Dental Medicine itself. From the response letter signed by the dean of the HSDM:

The magazine article states that CWF “does not appear to have any benefits in adults” based on the results of the Cochrane systematic review. However, the Cochrane review did not make this conclusion. Rather, the review specifically states “We did not identify any evidence, meeting the review’s inclusion criteria, to determine the effectiveness of water fluoridation for preventing caries in adults.” Due to the lack of studies that met the inclusion criteria, the Cochrane authors were not able to make any conclusion on the effect of CWF on adults. In fact, there are studies that were not included in the Cochrane review that demonstrate a caries preventive benefit of CWF in adults.

See the letter I linked for the studies it's referencing with a demonstrated benefit to adult teeth. The Cochrane review's inability to conclude whether there was a benefit or not was a limitation of the Cochrane review's inclusion criteria, and not an absence of studies indicating a benefit.

The internet do be like that sometimes, egos and the uninformed run free