Few topics stir up readers like fluoride.
Every time it's an issue, and it does make regular headlines, I get letters from all over the country, many accusing health authorities of terrible things like wanting to poison us all.
Maybe that's an exaggeration but it's not far from the general tone of the anti-fluoride brigade.
The wonderful thing about the internet is the access to a huge amount of information about any topic you choose. Anyone can become an expert. Sometimes that's also one of the worst things about the internet. Anyone can consider themselves experts.
When that "expertise" is based on something found in a far-flung corner of the internet, sourced from dodgy, partisan and/or discredited research, things get decidedly dicey.