What shady origins? It was done because because of the horrible state of dental health in the US.
"To join the armed services, men had to have six opposing teeth in their upper and lower jaws; in 1941, almost 10% of recruits were rejected for this reason alone"
Like it doesn't even matter if army recruits is a skewed sample, young men not having 6 pairs of teeth that touch is insane.
"In the early 1950s, two public health researchers stated that on average young men between the ages of 20 and 35 years had already lost an average of 4.2 teeth and that 90% of them were in need of bridges or full or partial dentures."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4504307/
The authoritative source of water fluoridation is https://www.york.ac.uk/media/crd/crdreport18.pdf which, broadly concludes that there isn't any strong evidence of harm.
