The source is not as reputable as it appears. The article in question is not from the Harvard School of Dental Medicine, and in fact was condemned by the HSDM. The actual dental experts at Harvard requested a formal retraction of the article: "Based on the significant flaws in the magazine article, we respectfully request that the article be rescinded, and a correction be published to clarify any misleading information that was provided."

Keep in mind that they listed Canada as having non-flouride water, presumably based on the sole criteria that it's not a national requirement. The split between communities with and without flouride in their water varies wildly by province.

It's an opinion piece by a geneticist (so not a chemist or biologist or a field that could be related) and she ignores all the direct evidence that every city and county that added fluoride started having fewer cavities than neighboring areas that hadn't yet added it.

She then further points out that it only causes health issues in much higher concentrations than what the US was getting our water supply up to. You know, like literally anything that you get too much of is bad for you. You can literally die from drinking too much plain water. Too much of anything will kill you.