You said you are an engineer and bragged about how smart you are, so I assumed you know how to do research. I'm not going to link every study out there. They are there and available. They do show high levels can be toxic, as with anything else. They also show appropriate levels save communities from tooth decay and the long-term issues those carry. I had faith that you know how to determine if a source is valid, and could do that on your own time. You can even go talk to a dentist and ask them for studies! They are a great resource, and I bet many of them would love to give you that information. I bet even a PCP office could point you in the direction of studies about the dangers and benefits of flouride.

Here's one for example, that explains how appropriate levels have helped and caused no harm. You being an engineer doesn't mean you aren't susceptible to disinformation campaigns. All of us are vulnerable to that sort of messaging, intelligence has nothing to do with it. Ignorance does, not being cognizant that there are people on TV and selling newspapers that have a vested interest in convincing people to harm their own communities and weaken their safety. Creating a bunch of tooth decay where none need be because you are not willing to read multiple sources on your own time and discern which ones are valid and which aren't, is a very weird behavior, to be honest with you.

Flourosis is a real issue, and it naturally occurs in waterways. We also use methods to control that. If we didn't have studies we wouldnt know that information either. We also know the lowest level possible to not cause harm and reduce dental issues in entire communities.

"To minimize fluoride toxicity, the concentration of fluoride in drinking water has been controlled to attain the recommended level of 0.8~1.0 ppm (13)"

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6195894/