Your link is more or less an opinion piece from a geneticist, so this isn't even her field of study.

All her health issues she points out are for fluoride concentrations over triple the amount that tap water is brought up to.

The reason it's usage spread across the country was because while the entire country had access to things such as fluoridated toothpaste, counties and cities that started fluoridation of their water supplies consistently had fewer cavities than areas that didn't fluoridate the water. This alone outlines the glaringly obvious flaw in her argument.

Further still, while the US adds fluoride to the tap water in a concentration to reach 0.5mg to 0.7mg per liter of water (a couple drops per 50 gallons), natural drinking water for over 20% of the world is in concentrations well over that (to be clear, being well over that can cause health issues. Too much of anything can cause health issues.)

In other words, there is no evidence that this low concentration of fluoride causes health issues. There is loads of direct evidence that it reduces cavities. Plus, this woman from your opinion piece is talking out of her field. Not to mention that 21% of the world's drinking water supply naturally already falls within the recommended range of what the US takes theirs up to. It's just that most of the US water supply naturally falls below that amount.